{{Short description|Indian mathematician (1887–1920)}}{{Redirect|Ramanujan}}{{pp-vandalism|small=yes}}{{Indian name|Ramanujan|Srinivasa}}{{Good article}}{{Use British English|date=September 2014}}{{Use dmy dates|date=April 2020}}

factoids

| image = File:Srinivasa Ramanujan-Add. MS a94 version2.jpgdf=yes12|22}}Erode, Mysore Princely State>Mysore State, British India (now in Tamil Nadu, India)df=yes4188722}}Kumbakonam, Tanjore District (Madras Presidency)>Tanjore District, Madras Presidency, British India (now Thanjavur district,Tamil Nadu, India)British Raj>British Indian| workplaces = University of Cambridge

• Government Arts College
• Pachaiyappa's College
• {{nowrap|Trinity College, Cambridge {{nowrap|(BA){edih}}}}}| thesis_title = Highly Composite Numbers| thesis_url =weblink" title="web.archive.org/web/20180809110104weblink">weblink| thesis_year = 1916

• G. H. Hardy
• J. E. Littlewood}}

• Ramanujan's sum
• Landau–Ramanujan constant
• Mock theta functions
• Ramanujan conjecture
• Ramanujan prime
• Ramanujan–Soldner constant
• Ramanujan theta function
• Rogers–Ramanujan identities
• Ramanujan's master theorem
• Hardy–Ramanujan asymptotic formula
• Ramanujan–Sato series{edih}| awards = Fellow of the Royal Society (1918)| signature = Signature of Srinivasa Ramanujan.svg| signature_alt = Srinivasa Ramanujan signature| field = Mathematics| doctoral_advisors =

}}Srinivasa Ramanujan{{efn|{{postnominals |FRS}} ({{IPAc-en|ˈ|s|r|iː|n|ᵻ|v|ɑː|s|ə|_|r|ɑː|ˈ|m|ɑː|n|ʊ|dʒ|ən}} {{respell|SREE|nih|vah|sə|_|rah|MAH|nuuj|ən}};BOOK, Olausson, Lena, Sangster, Catherine, 2006, Oxford BBC Guide to Pronunciation, Oxford University Press, 322, 978-0-19-280710-6, born Srinivasa Ramanujan Aiyangar, {{IPA-ta|sriːniʋaːsa ɾaːmaːnud͡ʑan ajːaŋgar|lang}})ODNB, 51582, Ramanujan, Srinivasa, 2004, Robert, Kanigel, WEB,weblink Ramanujan Aiyangar, Srinivasa (1887–1920), trove.nla.gov.au, }}(22 December 1887{{spaced ndash}}26 April 1920) was an Indian mathematician. Though he had almost no formal training in pure mathematics, he made substantial contributions to mathematical analysis, number theory, infinite series, and continued fractions, including solutions to mathematical problems then considered unsolvable.Ramanujan initially developed his own mathematical research in isolation. According to Hans Eysenck, "he tried to interest the leading professional mathematicians in his work, but failed for the most part. What he had to show them was too novel, too unfamiliar, and additionally presented in unusual ways; they could not be bothered".Hans Eysenck (1995). Genius, p. 197. Cambridge University Press, {{ISBN|0-521-48508-8}}. Seeking mathematicians who could better understand his work, in 1913 he began a mail correspondence with the English mathematician G. H. Hardy at the University of Cambridge, England. Recognising Ramanujan's work as extraordinary, Hardy arranged for him to travel to Cambridge. In his notes, Hardy commented that Ramanujan had produced groundbreaking new theorems, including some that "defeated me completely; I had never seen anything in the least like them before",BOOK, Hardy, Godfrey Harold, 1940, Ramanujan: Twelve Lectures on Subjects Suggested by His Life and Work, Cambridge University Press, 9, 0-8218-2023-0, and some recently proven but highly advanced results.During his short life, Ramanujan independently compiled nearly 3,900 results (mostly identities and equations).BOOK, Ramanujan's Notebooks, Part 5, Berndt, Bruce C., 12 December 1997, Springer Science & Business, 978-0-38794941-3, 4, Many were completely novel; his original and highly unconventional results, such as the Ramanujan prime, the Ramanujan theta function, partition formulae and mock theta functions, have opened entire new areas of work and inspired further research.JOURNAL, Ken Ono, Ono, Ken, June–July 2006, Honoring a Gift from Kumbakonam, Notices of the American Mathematical Society, 53, 6, 640–51 [649–50],weblink 2007-06-23, live,weblink 21 June 2007, Of his thousands of results, most have been proven correct.JOURNAL, August 1999, Rediscovering Ramanujan, Frontline (magazine), Frontline, 16, 17, 650,weblink 20 December 2012, dead,weblink" title="web.archive.org/web/20130925201456weblink">weblink 25 September 2013, The Ramanujan Journal, a scientific journal, was established to publish work in all areas of mathematics influenced by Ramanujan,BOOK, Analytic and Elementary Number Theory: A Tribute to Mathematical Legend Paul Erdos, Alladi, Krishnaswami, Elliott, P. D. T. A., Granville, A., 30 September 1998, Springer Science & Business, 978-0-79238273-7, 6, and his notebooks—containing summaries of his published and unpublished results—have been analysed and studied for decades since his death as a source of new mathematical ideas. As late as 2012, researchers continued to discover that mere comments in his writings about "simple properties" and "similar outputs" for certain findings were themselves profound and subtle number theory results that remained unsuspected until nearly a century after his death.Deep meaning in Ramanujan's 'simple' pattern {{webarchive |url=weblink |date=3 August 2017}}"Mathematical proof reveals magic of Ramanujan's genius" {{webarchive |url=weblink|date=9 July 2017}}. New Scientist. He became one of the youngest Fellows of the Royal Society and only the second Indian member, and the first Indian to be elected a Fellow of Trinity College, Cambridge.In 1919, ill health—now believed to have been hepatic amoebiasis (a complication from episodes of dysentery many years previously)—compelled Ramanujan's return to India, where he died in 1920 at the age of 32. His last letters to Hardy, written in January 1920, show that he was still continuing to produce new mathematical ideas and theorems. His "lost notebook", containing discoveries from the last year of his life, caused great excitement among mathematicians when it was rediscovered in 1976.

Early life

File:Erode, 18 Alahiri Str - Ramanujan birth place.jpg|thumb|upright|Ramanujan's birthplace on 18 Alahiri Street, Erode, now in Tamil NaduTamil NaduFile:Ramanujanhome.jpg|thumb|upright|Ramanujan's home on Sarangapani Sannidhi Street, KumbakonamKumbakonamRamanujan (literally, "younger brother of Rama", a Hindu deity){{harvnb|Kanigel|1991|page=12}} was born on 22 December 1887 into a Tamil Brahmin Iyengar family in Erode, in present-day Tamil Nadu.{{harvnb|Kanigel|1991|page=11}} His father, Kuppuswamy Srinivasa Iyengar, originally from Thanjavur district, worked as a clerk in a sari shop.{{harvnb|Kanigel|1991|pages=17–18}} His mother, Komalatammal, was a housewife and sang at a local temple.{{Harvnb|Berndt|Rankin|2001|p=89}} They lived in a small traditional home on Sarangapani Sannidhi Street in the town of Kumbakonam.NEWS, Srinivasan, Pankaja, The Nostalgia Formula,weblink 7 September 2016, The Hindu, 19 October 2012, The family home is now a museum. When Ramanujan was a year and a half old, his mother gave birth to a son, Sadagopan, who died less than three months later. In December 1889, Ramanujan contracted smallpox, but recovered, unlike the 4,000 others who died in a bad year in the Thanjavur district around this time. He moved with his mother to her parents' house in Kanchipuram, near Madras (now Chennai). His mother gave birth to two more children, in 1891 and 1894, both of whom died before their first birthdays.On 1 October 1892, Ramanujan was enrolled at the local school.{{harvnb|Kanigel|1991|page=13}} After his maternal grandfather lost his job as a court official in Kanchipuram,{{harvnb|Kanigel|1991|page=19}} Ramanujan and his mother moved back to Kumbakonam, and he was enrolled in Kangayan Primary School.{{harvnb|Kanigel|1991|page=14}} When his paternal grandfather died, he was sent back to his maternal grandparents, then living in Madras. He did not like school in Madras, and tried to avoid attending. His family enlisted a local constable to make sure he attended school. Within six months, Ramanujan was back in Kumbakonam.Since Ramanujan's father was at work most of the day, his mother took care of the boy, and they had a close relationship. From her, he learned about tradition and puranas, to sing religious songs, to attend pujas at the temple, and to maintain particular eating habits—all part of Brahmin culture.{{harvnb|Kanigel|1991|page=20}} At Kangayan Primary School, Ramanujan performed well. Just before turning 10, in November 1897, he passed his primary examinations in English, Tamil, geography, and arithmetic with the best scores in the district.{{harvnb|Kanigel|1991|page=25}} That year, Ramanujan entered Town Higher Secondary School, where he encountered formal mathematics for the first time.A child prodigy by age 11, he had exhausted the mathematical knowledge of two college students who were lodgers at his home. He was later lent a book written by S. L. Loney on advanced trigonometry.{{Harvnb|Berndt|Rankin|2001|p=9}}BOOK, Hardy, G. H., Ramanujan: Twelve Lectures on Subjects Suggested by His Life and Work, American Mathematical Society, Providence, Rhode Island, 1999, 978-0-8218-2023-0, 2, He mastered this by the age of 13 while discovering sophisticated theorems on his own. By 14, he received merit certificates and academic awards that continued throughout his school career, and he assisted the school in the logistics of assigning its 1,200 students (each with differing needs) to its approximately 35 teachers.{{harvnb|Kanigel|1991|page=27}} He completed mathematical exams in half the allotted time, and showed a familiarity with geometry and infinite series. Ramanujan was shown how to solve cubic equations in 1902. He would later develop his own method to solve the quartic. In 1903, he tried to solve the quintic, not knowing that it was impossible to solve with radicals.WEB, Srinivasa Ramanujan - Biography,weblink 2022-10-29, Maths History, en, In 1903, when he was 16, Ramanujan obtained from a friend a library copy of A Synopsis of Elementary Results in Pure and Applied Mathematics, G. S. Carr's collection of 5,000 theorems.{{harvnb|Kanigel|1991|page=39}}McElroy, Tucker (2005). A to Z of mathematicians. Facts on File. p. 221. {{isbn|0-8160-5338-3-}} Ramanujan reportedly studied the contents of the book in detail.{{citation | title= Collected papers of Srinivasa Ramanujan | journal=Nature | volume=123 | issue=3104 | first1=Srinivasa | last1=Ramanujan Aiyangar | first2= Godfrey Harold | last2= Hardy | first3= P. Veṅkatesvara Seshu |last3=Aiyar |year= 2000 |isbn= 978-0-8218-2076-6 |page= xii| bibcode=1929Natur.123..631L | doi=10.1038/123631a0 | s2cid=44812911 }} The next year, Ramanujan independently developed and investigated the Bernoulli numbers and calculated the Euler–Mascheroni constant up to 15 decimal places.{{harvnb|Kanigel|1991|page=90}} His peers at the time said they "rarely understood him" and "stood in respectful awe" of him.When he graduated from Town Higher Secondary School in 1904, Ramanujan was awarded the K. Ranganatha Rao prize for mathematics by the school's headmaster, Krishnaswami Iyer. Iyer introduced Ramanujan as an outstanding student who deserved scores higher than the maximum.{{harvnb|Kanigel|1991|page=??}} He received a scholarship to study at Government Arts College, Kumbakonam,{{harvnb|Kanigel|1991|page=28}}{{harvnb|Kanigel|1991|page=45}} but was so intent on mathematics that he could not focus on any other subjects and failed most of them, losing his scholarship in the process.{{harvnb|Kanigel|1991|pages=47–48}} In August 1905, Ramanujan ran away from home, heading towards Visakhapatnam, and stayed in RajahmundryNEWS,weblink Chennai, India, The Hindu, Ramanujan lost and found: a 1905 letter from The Hindu, 25 December 2011, for about a month. He later enrolled at Pachaiyappa's College in Madras. There, he passed in mathematics, choosing only to attempt questions that appealed to him and leaving the rest unanswered, but performed poorly in other subjects, such as English, physiology, and Sanskrit.NEWS, Krishnamachari, Suganthi, Travails of a Genius,weblink 7 September 2016, The Hindu, 27 June 2013, live,weblink 26 August 2017, Ramanujan failed his Fellow of Arts exam in December 1906 and again a year later. Without an FA degree, he left college and continued to pursue independent research in mathematics, living in extreme poverty and often on the brink of starvation.{{harvnb|Kanigel|1991|page=55–56}}In 1910, after a meeting between the 23-year-old Ramanujan and the founder of the Indian Mathematical Society, V. Ramaswamy Aiyer, Ramanujan began to get recognition in Madras's mathematical circles, leading to his inclusion as a researcher at the University of Madras.WEB, Krishnamurthy, V., Srinivasa Ramanujan – His life and his genius,weblink www.krishnamurthys.com, (Expository address delivered on Sep.16, 1987 at Visvesvarayya Auditorium as part of the celebrations of Ramanujan Centenary by the IISC, Bangalore), 7 September 2016, dead,weblink 21 September 2016,

Adulthood in India

On 14 July 1909, Ramanujan married Janaki (Janakiammal; 21 March 1899 – 13 April 1994),WEB, Live mint,weblink The seamstress and the mathematician, 20 April 2018, a girl his mother had selected for him a year earlier and who was ten years old when they married.>{{harvnb|Kanigel|1991|page=71}}BOOK, Bullough, V.L., 2. History in adult human sexual behavior with children and adolescents in Western societies, 1990, Springer-Verlag, New York, 978-1-46139684-0, 71, Pedophilia: Biosocial Dimensions,weblink JOURNAL, Kolata, Gina, Gina Kolata, 19 June 1987, Remembering a 'Magical Genius', Science, New Series, 236, 4808, 1519–21, 10.1126/science.236.4808.1519, 17835731, 1987Sci...236.1519K, It was not unusual then for marriages to be arranged with girls at a young age. Janaki was from Rajendram, a village close to Marudur (Karur district) Railway Station. Ramanujan's father did not participate in the marriage ceremony.WEB, Ramanujan's wife: Janakiammal (Janaki),weblink Institute of Mathematical Sciences, Chennai, 10 November 2012, dead,weblink 24 December 2012, As was common at that time, Janaki continued to stay at her maternal home for three years after marriage, until she reached puberty. In 1912, she and Ramanujan's mother joined Ramanujan in Madras.NEWS, Janardhanan, Arun, A passage to infinity,weblink 7 September 2016, Indian Express, 6 December 2015, live,weblink 5 September 2016, (File:Ramanujan seated alone.png|thumb|Ramanujan seated alone)After the marriage, Ramanujan developed a hydrocele testis.>{{harvnb|Kanigel|1991|page=72}} The condition could be treated with a routine surgical operation that would release the blocked fluid in the scrotal sac, but his family could not afford the operation. In January 1910, a doctor volunteered to do the surgery at no cost.BOOK, Ramanujan, Srinivasa, P. K. Srinivasan, Ramanujan Memorial Number: Letters and Reminiscences, 1968, Muthialpet High School, Madras, 100, 1, true, After his successful surgery, Ramanujan searched for a job. He stayed at a friend's house while he went from door to door around Madras looking for a clerical position. To make money, he tutored students at Presidency College who were preparing for their Fellow of Arts exam.{{harvnb|Kanigel|1991|page=73}}In late 1910, Ramanujan was sick again. He feared for his health, and told his friend R. Radakrishna Iyer to "hand [his notebooks] over to Professor Singaravelu Mudaliar [the mathematics professor at Pachaiyappa's College] or to the British professor Edward B. Ross, of the Madras Christian College."{{harvnb|Kanigel|1991|pages=74–75}} After Ramanujan recovered and retrieved his notebooks from Iyer, he took a train from Kumbakonam to Villupuram, a city under French control.BOOK, Ranganathan, Shiyali Ramamrita, Shiyali Ramamrita Ranganathan, Ramanujan: The Man and the Mathematician, 1967, Asia Publishing House, Bombay,weblink 23, 9788185273372, Srinivasan (1968), Vol. 1, p. 99. In 1912, Ramanujan moved with his wife and mother to a house in Saiva Muthaiah Mudali street, George Town, Madras, where they lived for a few months.WEB, Rao, K. Srinivasa, Ramanujan's wife Janakiammal (Janaki),weblink IMSC, Institute of Mathematical Sciences, Chennai, 7 September 2016, dead,weblink 10 January 2017, In May 1913, upon securing a research position at Madras University, Ramanujan moved with his family to Triplicane.WEB, About Ramanujan,weblink The Ramanujan Institute, 7 September 2016, dead,weblink 6 October 2016,

Pursuit of career in mathematics

In 1910, Ramanujan met deputy collector V. Ramaswamy Aiyer, who founded the Indian Mathematical Society.{{harvnb|Kanigel|1991|page=77}} Wishing for a job at the revenue department where Aiyer worked, Ramanujan showed him his mathematics notebooks. As Aiyer later recalled:I was struck by the extraordinary mathematical results contained in [the notebooks]. I had no mind to smother his genius by an appointment in the lowest rungs of the revenue department.Srinivasan (1968), Vol. 1, p. 129.Aiyer sent Ramanujan, with letters of introduction, to his mathematician friends in Madras. Some of them looked at his work and gave him letters of introduction to R. Ramachandra Rao, the district collector for Nellore and the secretary of the Indian Mathematical Society.Srinivasan (1968), Vol. 1, p. 86.JOURNAL, Neville, Eric Harold, January 1921, The Late Srinivasa Ramanujan, Nature (journal), Nature, 106, 2673, 661–662, 10.1038/106661b0, 1921Natur.106..661N, 4185656,weblink {{Harvnb|Ranganathan|1967|p=24}} Rao was impressed by Ramanujan's research but doubted that it was his own work. Ramanujan mentioned a correspondence he had with Professor Saldhana, a notable Bombay mathematician, in which Saldhana expressed a lack of understanding of his work but concluded that he was not a fraud.{{harvnb|Kanigel|1991|page=80}} Ramanujan's friend C. V. Rajagopalachari tried to quell Rao's doubts about Ramanujan's academic integrity. Rao agreed to give him another chance, and listened as Ramanujan discussed elliptic integrals, hypergeometric series, and his theory of divergent series, which Rao said ultimately convinced him of Ramanujan's brilliance. When Rao asked him what he wanted, Ramanujan replied that he needed work and financial support. Rao consented and sent him to Madras. He continued his research with Rao's financial aid. With Aiyer's help, Ramanujan had his work published in the ''Journal of the Indian Mathematical Society.{{harvnb|Kanigel|1991|page=86}} (File:K Ananda Rau seated with Ramanujan.jpg|thumb|K Ananda Rau seated with Ramanujan) One of the first problems he posed in the journal was to find the value of: He waited for a solution to be offered in three issues, over six months, but failed to receive any. At the end, Ramanujan supplied an incompleteJOURNAL, Herschfeld, Aaron, August 1935, On Infinite Radicals,weblink The American Mathematical Monthly, en, 42, 7, 419–429, 10.1080/00029890.1935.11987745, 0002-9890, solution to the problem himself. On page 105 of his first notebook, he formulated an equation that could be used to solve the infinitely nested radicals problem. Using this equation, the answer to the question posed in the Journal was simply 3, obtained by setting {{math|1=x = 2}}, {{math|1=n = 1}}, and {{math|1=a = 0}}.{{harvnb|Kanigel|1991|page=87}} Ramanujan wrote his first formal paper for the Journal on the properties of Bernoulli numbers. One property he discovered was that the denominators of the fractions of Bernoulli numbers {{OEIS|id=A027642}} are always divisible by six. He also devised a method of calculating {{mvar|Bn}} based on previous Bernoulli numbers. One of these methods follows:It will be observed that if n is even but not equal to zero,

1. {{mvar|Bn}} is a fraction and the numerator of {{math|{{sfrac|Bn|n}}}} in its lowest terms is a prime number,
2. the denominator of {{mvar|Bn}} contains each of the factors 2 and 3 once and only once,
3. {{math|2n(2n − 1){{sfrac|Bn|n}}}} is an integer and {{math|2(2n − 1)Bn}} consequently is an odd integer.

In his 17-page paper "Some Properties of Bernoulli's Numbers" (1911), Ramanujan gave three proofs, two corollaries and three conjectures.{{harvnb|Kanigel|1991|page=91}} His writing initially had many flaws. As Journal editor M. T. Narayana Iyengar noted:Mr. Ramanujan's methods were so terse and novel and his presentation so lacking in clearness and precision, that the ordinary [mathematical reader], unaccustomed to such intellectual gymnastics, could hardly follow him.JOURNAL, Seshu Iyer, P. V., June 1920, The Late Mr. S. Ramanujan, B.A., F.R.S., Journal of the Indian Mathematical Society, 12, 3, 83, Ramanujan later wrote another paper and also continued to provide problems in the Journal. In early 1912, he got a temporary job in the Madras Accountant General's office, with a monthly salary of 20 rupees. He lasted only a few weeks.Srinivasan (1968), p. 176. Toward the end of that assignment, he applied for a position under the Chief Accountant of the Madras Port Trust.In a letter dated 9 February 1912, Ramanujan wrote:Sir,{{pad|2em}}I understand there is a clerkship vacant in your office, and I beg to apply for the same. I have passed the Matriculation Examination and studied up to the F.A. but was prevented from pursuing my studies further owing to several untoward circumstances. I have, however, been devoting all my time to Mathematics and developing the subject. I can say I am quite confident I can do justice to my work if I am appointed to the post. I therefore beg to request that you will be good enough to confer the appointment on me.Srinivasan (1968), p. 31.Attached to his application was a recommendation from E. W. Middlemast, a mathematics professor at the Presidency College, who wrote that Ramanujan was "a young man of quite exceptional capacity in Mathematics".Srinivasan (1968), p. 49. Three weeks after he applied, on 1 March, Ramanujan learned that he had been accepted as a Class III, Grade IV accounting clerk, making 30 rupees per month.{{harvnb|Kanigel|1991|page=96}} At his office, Ramanujan easily and quickly completed the work he was given and spent his spare time doing mathematical research. Ramanujan's boss, Sir Francis Spring, and S. Narayana Iyer, a colleague who was also treasurer of the Indian Mathematical Society, encouraged Ramanujan in his mathematical pursuits.{{sfnp|Berndt|Rankin|2001|p=97}}

Contacting British mathematicians

In the spring of 1913, Narayana Iyer, Ramachandra Rao and E. W. Middlemast tried to present Ramanujan's work to British mathematicians. M. J. M. Hill of University College London commented that Ramanujan's papers were riddled with holes.{{harvnb|Kanigel|1991|page=105}} He said that although Ramanujan had "a taste for mathematics, and some ability", he lacked the necessary educational background and foundation to be accepted by mathematicians.Letter from M. J. M. Hill to a C. L. T. Griffith (a former student who sent the request to Hill on Ramanujan's behalf), 28 November 1912. Although Hill did not offer to take Ramanujan on as a student, he gave thorough and serious professional advice on his work. With the help of friends, Ramanujan drafted letters to leading mathematicians at Cambridge University.{{harvnb|Kanigel|1991|page=106}}The first two professors, H. F. Baker and E. W. Hobson, returned Ramanujan's papers without comment.{{harvnb|Kanigel|1991|pages=170–171}} On 16 January 1913, Ramanujan wrote to G. H. Hardy.WEB,weblink The letter that revealed Ramanujan's genius, YouTube, Coming from an unknown mathematician, the nine pages of mathematics made Hardy initially view Ramanujan's manuscripts as a possible fraud.BOOK, Snow, C. P., Variety of Men, 1966, Charles Scribner's Sons, New York, 30–31, Hardy recognised some of Ramanujan's formulae but others "seemed scarcely possible to believe".JOURNAL, Hardy, G. H., G. H. Hardy, 1920, Obituary, S. Ramanujan, Nature, 105, 7, 494–495, 10.1038/105494a0, 1920Natur.105..494H, 4174904,weblink free, {{rp|494}} One of the theorems Hardy found amazing was on the bottom of page three (valid for {{math|0 < a < b + {{sfrac|1|2}}}}): intlimits_0^infty frac{1+dfrac{x^2}{(b+1)^2}}{1+dfrac{x^2}{a^2}} timesfrac{1+dfrac{x^2}{(b+2)^2}}{1+dfrac{x^2}{(a+1)^2}}timescdots,dx

frac{sqrt pi}{2} timesfrac{Gammaleft(a+frac12right) Gamma(b+1) Gamma(b-a+1)}{Gamma(a)Gammaleft(b+frac12right)Gammaleft(b-a + frac12 right)}.

Hardy was also impressed by some of Ramanujan's other work relating to infinite series: The first result had already been determined by G. Bauer in 1859. The second was new to Hardy, and was derived from a class of functions called hypergeometric series, which had first been researched by Euler and Gauss. Hardy found these results "much more intriguing" than Gauss's work on integrals.{{harvnb|Kanigel|1991|page=167}} After seeing Ramanujan's theorems on continued fractions on the last page of the manuscripts, Hardy said the theorems "defeated me completely; I had never seen anything in the least like them before",{{harvnb|Kanigel|1991|page=168}} and that they "must be true, because, if they were not true, no one would have the imagination to invent them". Hardy asked a colleague, J. E. Littlewood, to take a look at the papers. Littlewood was amazed by Ramanujan's genius. After discussing the papers with Littlewood, Hardy concluded that the letters were "certainly the most remarkable I have received" and that Ramanujan was "a mathematician of the highest quality, a man of altogether exceptional originality and power".{{rp|494–495}} One colleague, E. H. Neville, later remarked that "not one [theorem] could have been set in the most advanced mathematical examination in the world".JOURNAL, Neville, Eric Harold, 1942, Srinivasa Ramanujan, Nature, 149, 3776, 292–293, 10.1038/149292a0, 1942Natur.149..292N, free, On 8 February 1913, Hardy wrote Ramanujan a letter expressing interest in his work, adding that it was "essential that I should see proofs of some of your assertions".Letter, Hardy to Ramanujan, 8 February 1913. Before his letter arrived in Madras during the third week of February, Hardy contacted the Indian Office to plan for Ramanujan's trip to Cambridge. Secretary Arthur Davies of the Advisory Committee for Indian Students met with Ramanujan to discuss the overseas trip.Letter, Ramanujan to Hardy, 22 January 1914. In accordance with his Brahmin upbringing, Ramanujan refused to leave his country to "go to a foreign land".{{harvnb|Kanigel|1991|page=185}} Meanwhile, he sent Hardy a letter packed with theorems, writing, "I have found a friend in you who views my labour sympathetically."Letter, Ramanujan to Hardy, 27 February 1913, Cambridge University Library.To supplement Hardy's endorsement, Gilbert Walker, a former mathematical lecturer at Trinity College, Cambridge, looked at Ramanujan's work and expressed amazement, urging the young man to spend time at Cambridge.{{harvnb|Kanigel|1991|page=175}} As a result of Walker's endorsement, B. Hanumantha Rao, a mathematics professor at an engineering college, invited Ramanujan's colleague Narayana Iyer to a meeting of the Board of Studies in Mathematics to discuss "what we can do for S. Ramanujan".BOOK, Ram, Suresh, Srinivasa Ramanujan, 1972, National Book Trust, New Delhi, 29, The board agreed to grant Ramanujan a monthly research scholarship of 75 rupees for the next two years at the University of Madras.{{Harvnb|Ranganathan|1967|pp=30–31}}While he was engaged as a research student, Ramanujan continued to submit papers to the Journal of the Indian Mathematical Society. In one instance, Iyer submitted some of Ramanujan's theorems on summation of series to the journal, adding, "The following theorem is due to S. Ramanujan, the mathematics student of Madras University." Later in November, British Professor Edward B. Ross of Madras Christian College, whom Ramanujan had met a few years before, stormed into his class one day with his eyes glowing, asking his students, "Does Ramanujan know Polish?" The reason was that in one paper, Ramanujan had anticipated the work of a Polish mathematician whose paper had just arrived in the day's mail.{{Harvnb|Ranganathan|1967|p=12}} In his quarterly papers, Ramanujan drew up theorems to make definite integrals more easily solvable. Working off Giuliano Frullani's 1821 integral theorem, Ramanujan formulated generalisations that could be made to evaluate formerly unyielding integrals.{{harvnb|Kanigel|1991|page=183}}Hardy's correspondence with Ramanujan soured after Ramanujan refused to come to England. Hardy enlisted a colleague lecturing in Madras, E. H. Neville, to mentor and bring Ramanujan to England.{{harvnb|Kanigel|1991|page=184}} Neville asked Ramanujan why he would not go to Cambridge. Ramanujan apparently had now accepted the proposal; Neville said, "Ramanujan needed no converting" and "his parents' opposition had been withdrawn". Apparently, Ramanujan's mother had a vivid dream in which the family goddess, the deity of Namagiri, commanded her "to stand no longer between her son and the fulfilment of his life's purpose". On 17 March 1914, Ramanujan traveled to England by ship,WEB, A (very) Brief History of Srinivasa Ramanujan, YouTube,weblinkweblink 2021-12-11, live, {{cbignore}} leaving his wife to stay with his parents in India.{{sfnp|Berndt|Rankin|2001|pp=83–84}}

Life in England

File:RamanujanCambridge.jpg|thumb|upright=1.3|Ramanujan (centre) and his colleague G. H. Hardy (rightmost), with other scientists, outside the Senate House, CambridgeSenate House, CambridgeFile:Whewell's Court, Trinity College, Cambridge.jpg|thumb|upright|Whewell's Court, Trinity College, CambridgeTrinity College, CambridgeRamanujan departed from Madras aboard the S.S. Nevasa on 17 March 1914.{{harvnb|Kanigel|1991|page=196}} When he disembarked in London on 14 April, Neville was waiting for him with a car. Four days later, Neville took him to his house on Chesterton Road in Cambridge. Ramanujan immediately began his work with Littlewood and Hardy. After six weeks, Ramanujan moved out of Neville's house and took up residence on Whewell's Court, a five-minute walk from Hardy's room.{{harvnb|Kanigel|1991|page=202}} (File:Ramanujan's "Master Theorem" page.jpg|thumb|Ramanujan's "Master Theorem" page)Hardy and Littlewood began to look at Ramanujan's notebooks. Hardy had already received 120 theorems from Ramanujan in the first two letters, but there were many more results and theorems in the notebooks. Hardy saw that some were wrong, others had already been discovered, and the rest were new breakthroughs.BOOK, Hardy, G. H., Ramanujan, 1940, Cambridge University Press, Cambridge, 10, Ramanujan left a deep impression on Hardy and Littlewood. Littlewood commented, "I can believe that he's at least a Jacobi",Letter, Littlewood to Hardy, early March 1913. while Hardy said he "can compare him only with Euler or Jacobi."BOOK, Hardy, G. H., Collected Papers of G. H. Hardy, 1979, Oxford University Press, Clarendon Press, Oxford, England, 720, 7, true, Ramanujan spent nearly five years in Cambridge collaborating with Hardy and Littlewood, and published part of his findings there. Hardy and Ramanujan had highly contrasting personalities. Their collaboration was a clash of different cultures, beliefs, and working styles. In the previous few decades, the foundations of mathematics had come into question and the need for mathematically rigorous proofs recognised. Hardy was an atheist and an apostle of proof and mathematical rigour, whereas Ramanujan was a deeply religious man who relied very strongly on his intuition and insights. Hardy tried his best to fill the gaps in Ramanujan's education and to mentor him in the need for formal proofs to support his results, without hindering his inspiration—a conflict that neither found easy.Ramanujan was awarded a Bachelor of Arts by Research degreeThe Cambridge University Reporter, of 18 March 1916, reports: Bachelors designate in Arts, Srinivasa Ramanujan (Research Student), Trin.A clear photographic image of said document can be viewed on the following YouTube video at the specified timestampweblink The Maths PhD in the UK: Notes on its History,weblink 2020-08-09, www.economics.soton.ac.uk, (the predecessor of the PhD degree) in March 1916 for his work on highly composite numbers, sections of the first part of which had been published the preceding year in the Proceedings of the London Mathematical Society. The paper was more than 50 pages long and proved various properties of such numbers. Hardy disliked this topic area but remarked that though it engaged with what he called the 'backwater of mathematics', in it Ramanujan displayed 'extraordinary mastery over the algebra of inequalities'.Jean-Louis Nicolas, Guy Robin (eds.), Highly Composite Numbers by Srinivasa Ramanujan, The Ramanujan Journal 1997 1, 119–153, p.121On 6 December 1917, Ramanujan was elected to the London Mathematical Society. On 2 May 1918, he was elected a Fellow of the Royal Society,WEB, Embleton, Ellen, Revisiting Ramanujan,weblink The Royal Society, 16 February 2020, 2 October 2018, 16 February 2020,weblink dead, the second Indian admitted, after Ardaseer Cursetjee in 1841. At age 31, Ramanujan was one of the youngest Fellows in the Royal Society's history. He was elected "for his investigation in elliptic functions and the Theory of Numbers." On 13 October 1918, he was the first Indian to be elected a Fellow of Trinity College, Cambridge.{{harvnb|Kanigel|1991|pages=299–300}}

Illness and death

Ramanujan had numerous health problems throughout his life. His health worsened in England; possibly he was also less resilient due to the difficulty of keeping to the strict dietary requirements of his religion there and because of wartime rationing in 1914–18. He was diagnosed with tuberculosis and a severe vitamin deficiency, and confined to a sanatorium. In 1919, he returned to Kumbakonam, Madras Presidency, and in 1920 he died at the age of 32. After his death, his brother Tirunarayanan compiled Ramanujan's remaining handwritten notes, consisting of formulae on singular moduli, hypergeometric series and continued fractions.Ramanujan's widow, Smt. Janaki Ammal, moved to Bombay. In 1931, she returned to Madras and settled in Triplicane, where she supported herself on a pension from Madras University and income from tailoring. In 1950, she adopted a son, W. Narayanan, who eventually became an officer of the State Bank of India and raised a family. In her later years, she was granted a lifetime pension from Ramanujan's former employer, the Madras Port Trust, and pensions from, among others, the Indian National Science Academy and the state governments of Tamil Nadu, Andhra Pradesh and West Bengal. She continued to cherish Ramanujan's memory, and was active in efforts to increase his public recognition; prominent mathematicians, including George Andrews, Bruce C. Berndt and Béla Bollobás made it a point to visit her while in India. She died at her Triplicane residence in 1994.A 1994 analysis of Ramanujan's medical records and symptoms by D. A. B. YoungJOURNAL, 10.1098/rsnr.1994.0009, Young, D. A. B., 1994, Ramanujan's illness, Notes and Records of the Royal Society of London, 48, 1, 107–119, 11615274, 33416179, concluded that his medical symptoms—including his past relapses, fevers, and hepatic conditions—were much closer to those resulting from hepatic amoebiasis, an illness then widespread in Madras, than tuberculosis. He had two episodes of dysentery before he left India. When not properly treated, amoebic dysentery can lie dormant for years and lead to hepatic amoebiasis, whose diagnosis was not then well established.WEB,weblink Raiders of the Lost Notebook, 11 January 2014, Peterson, Doug, UIUC College of Liberal Arts and Sciences, dead,weblink 12 January 2014, At the time, if properly diagnosed, amoebiasis was a treatable and often curable disease;JOURNAL, Gunn, J. W. C., Savage, B., 1919, Report on the treatment of Entamoeba histolytica infections, Journal of the Royal Army Medical Corps, 33, 5, 418–426, British soldiers who contracted it during the First World War were being successfully cured of amoebiasis around the time Ramanujan left England.JOURNAL, Langley, George J., 20429465, The Difficulties in Diagnosis And Treatment of Hepatic Abscess, British Medical Journal, 2, 3182, 1073–1074, 24 December 1921, 20770524, 2339657, 10.1136/bmj.2.3182.1073,

Personality and spiritual life

}}Ramanujan has been described as a person of a somewhat shy and quiet disposition, a dignified man with pleasant manners.WEB,weblink Ramanujan's Personality, dead,weblink 27 September 2007, dmy-all, 23 June 2018, He lived a simple life at Cambridge.{{harvnb|Kanigel|1991|pages=234, 241}} Ramanujan's first Indian biographers describe him as a rigorously orthodox Hindu. He credited his acumen to his family goddess, Namagiri Thayar (Goddess Mahalakshmi) of Namakkal. He looked to her for inspiration in his work{{harvnb|Kanigel|1991|page=36}} and said he dreamed of blood drops that symbolised her consort, Narasimha. Later he had visions of scrolls of complex mathematical content unfolding before his eyes.{{harvnb|Kanigel|1991|page=281}} He often said, "An equation for me has no meaning unless it expresses a thought of God."JOURNAL, Less Proof, More Truth, New Scientist, 2614, 28 July 2007, 49, Chaitin, Gregory, 10.1016/S0262-4079(07)61908-3,weblink Hardy cites Ramanujan as remarking that all religions seemed equally true to him.{{harvnb|Kanigel|1991|page=283}} Hardy further argued that Ramanujan's religious belief had been romanticised by Westerners and overstated—in reference to his belief, not practice—by Indian biographers. At the same time, he remarked on Ramanujan's strict vegetarianism.{{Harvnb|Berndt|Rankin|2001|p=47}}Similarly, in an interview with Frontline, Berndt said, "Many people falsely promulgate mystical powers to Ramanujan's mathematical thinking. It is not true. He has meticulously recorded every result in his three notebooks," further speculating that Ramanujan worked out intermediate results on slate that he could not afford the paper to record more permanently.

Mathematical achievements

In mathematics, there is a distinction between insight and formulating or working through a proof. Ramanujan proposed an abundance of formulae that could be investigated later in depth. G. H. Hardy said that Ramanujan's discoveries are unusually rich and that there is often more to them than initially meets the eye. As a byproduct of his work, new directions of research were opened up. Examples of the most intriguing of these formulae include infinite series for {{pi}}, one of which is given below: This result is based on the negative fundamental discriminant {{nowrap|1={{mvar|d}} = −4 × 58 = −232}} with class number {{nowrap|1={{math|h(d)}} = 2}}. Further, {{nowrap|1=26390 = 5 × 7 × 13 × 58}} and {{nowrap|1=16 × 9801 = 3962}}, which is related to the fact that This might be compared to Heegner numbers, which have class number 1 and yield similar formulae.Ramanujan's series for {{pi}} converges extraordinarily rapidly and forms the basis of some of the fastest algorithms currently used to calculate {{pi}}. Truncating the sum to the first term also gives the approximation {{sfrac|9801{{sqrt|2}}|4412}} for {{pi}}, which is correct to six decimal places; truncating it to the first two terms gives a value correct to 14 decimal places {{xref|(see also the more general Ramanujan–Sato series)}}.One of Ramanujan's remarkable capabilities was the rapid solution of problems, illustrated by the following anecdote about an incident in which P. C. Mahalanobis posed a problem:{{blockquote|Imagine that you are on a street with houses marked 1 through {{mvar|n}}. There is a house in between ({{mvar|x}}) such that the sum of the house numbers to the left of it equals the sum of the house numbers to its right. If {{mvar|n}} is between 50 and 500, what are {{mvar|n}} and {{mvar|x}}?' This is a bivariate problem with multiple solutions. Ramanujan thought about it and gave the answer with a twist: He gave a continued fraction. The unusual part was that it was the solution to the whole class of problems. Mahalanobis was astounded and asked how he did it. 'It is simple. The minute I heard the problem, I knew that the answer was a continued fraction. Which continued fraction, I asked myself. Then the answer came to my mind', Ramanujan replied."{{Harvnb|Ranganathan|1967|p=82}}BOOK, Statistics and truth: putting chance to work, 1997, World Scientific,weblink Calyampudi Radhakrishna Rao, 7 June 2010, 185, 978-981-02-3111-8, }}His intuition also led him to derive some previously unknown identities, such as begin{align}& left ( 1+2sum_{n=1}^infty frac{cos(ntheta)}{cosh(npi)} right )^{-2} + left (1+2sum_{n=1}^infty frac{cosh(ntheta)}{cosh(npi)} right )^{-2} [6pt]

{} & frac {2 Gamma^4 bigl( frac34 bigr)} pi frac{8pi^3}{Gamma^4 bigl( frac14 bigr)}

end{align}for all {{math|θ}} such that |Re (theta)|