In March 1918, at the peak of both the First World War and the British Raj, Britain's Royal Society elected as a fellow Srinivasa Ramanujan. Born in 1887 into an undistinguished family of Tamil Brahmins, Ramanujan was a penurious former accounts clerk at the Madras Port Trust who had failed to obtain any university degree in India but who had somehow created important but largely unproven mathematical theorems. In 1913, desperate for recognition, he mailed some of these out of the blue to a leading British mathematician, G. H. Hardy, who was so fascinated by them that he invited Ramanujan to Cambridge University. “The limitations of his knowledge were as startling as its profundity”, Hardy wrote after Ramanujan's death in 1920. “His ideas as to what constituted a mathematical proof were of the most shadowy description. All his results, new and old, right or wrong, had been arrived at by a process of mingled argument, intuition and induction, of which he was entirely unable to give any coherent account”. Eventually, after collaborating with Hardy, Ramanujan proved his worth as a mathematician: one of the great mathematicians of all time, it is now generally accepted, whose theorems yield new and surprising discoveries a century after his premature departure at the age of only 32.

Ramanujan was only the second Indian to be elected an FRS, and the very first since the reform of the Royal Society in the mid-nineteenth century into an organisation of professional scientists, rather than gentleman scholars with aristocratic connections. Other Indians followed his lead during the twentieth century, including C. V. Raman, the first Indian Nobel laureate in science. In 2015, the society elected its first Indian-born president, the Nobel prize-winning structural biologist Venkatraman Ramakrishnan. Appropriately, Ramakrishnan presided over the launch of a new feature film about Ramanujan, The Man Who Knew Infinity—based on the US academic Robert Kanigel's compelling 1991 biography of the same title—at the London offices of the Royal Society in 2016. I attended and casually asked Ramakrishnan what he thought present-day India could learn from Ramanujan's astonishing life-story. Not much, he implied—because Ramanujan was unique.

The Japanese-American mathematician Ken Ono—whose career in US universities has been dedicated to exploring Ramanujan's theorems, notably the Rogers-Ramanujan identities, and who acted as the mathematics adviser to the actors playing Ramanujan and Hardy in The Man Who Knew Infinity—would surely not disagree with this candid assessment. And yet, Ramanujan radically changed Ono's life. Ramanujan's unique career in the 1910s saved Ono from both personal and professional crisis in the 1990s, as he describes in his intriguing and sometimes moving memoir, My Search for Ramanujan, with its ironic and touching subtitle, How I Learned to Count.

Written with the assistance of science writer Amir Aczel (author of Fermat's Last Theorem), who sadly died just before publication, My Search for Ramanujan interweaves Ramanujan's life and mathematics with Ono's own struggle to become a mathematician—including a suicide attempt in 1992 (ditto Ramanujan in 1918)—in the shadow of his hard-driving Japanese-American ‘tiger’ parents, especially his distant mathematician father, Takashi Ono, born in Japan in 1928. They—with the help of a distinguished French-American mathematician, André Weil—emigrated from war-devastated Japan in the late 1950s to the United States, where they suffered from considerable racial prejudice and retained their Japanese citizenship until 2007. Their son Ken, born a US citizen in 1968, remembers his home life as a child as “a small-scale version of isolationist Japan during the Tokugawa period (1641-1853), when the shoguns, leaders of the military government, enforced a policy called kaikin, which largely prohibited contact with foreign countries. The original edict that enforced this policy had 17 rules, including one that Japanese who secretly attempted to travel abroad were to be executed, and any Japanese residing abroad who returned to Japan were also to be executed”.

Then, one day in 1984, Ken's father received a letter on delicate rice paper from Madras, which is reproduced in Ono's book. Uncharacteristically, he shared it with his rebellious teenaged son. “Dear Sir”, it read. “I understand from Mr. Richard Askey, Wisconsin, U.S.A., that you have contributed for the sculpture in memory of my late husband Mr. Srinivasa Ramanujan. I am happy over this event. I thank you very much for your good gesture and wish you success in all your endeavours”. Signed “S. Janaki Ammal”, it came from Ramanujan's widow, now a destitute woman in her eighties who had cherished the wish for a statue of Ramanujan ever since his death. Not surprisingly, the letter, and the name Ramanujan, meant nothing to Ono junior. “Who's this guy Ramanujan? What did he do?” But after Ono senior told him Ramanujan's story, Ken recognised that his father was deeply stirred by the letter because in many ways his own life had mirrored that of the Indian mathematician. Like Ramanujan in India, Takashi Ono had been rescued from dire straits in Japan by his talent for mathematics and been taken abroad through the generosity of a foreign mathematician. And like Ramanujan in Britain, Ono senior had been rewarded in the United States for his achievements “despite the indignities and hindrances to success that they suffer[ed] due to racial prejudice”, writes Ono.

For his own life, the letter turned out to be a passport to independence. After months of heated shouting matches with his parents, Ken finally cited Ramanujan to his father as an example of a successful college dropout, and was allowed to go his own way. At the time, he was greatly surprised that his father gave in. Only in 1997, after he had started to make his own mark as a professional mathematician in the eyes of his father, did he discover the reason, when Takashi Ono introduced him to his 1950s mentor, Weil, then aged 91. It turned out that Weil, too, had long been an aficionado of Ramanujan, and had told his young Japanese colleagues, including Takashi, the inspiring story of the Indian mathematician in an impromptu after-dinner talk at a mathematics conference in Tokyo in 1955. After long years of estrangement, Ono junior and senior at last realised that they were bound together by admiration and affection for Ramanujan. “The enigmatic Ramanujan had helped make my father”, writes Ono, “and because of that, he was somehow helping to make something of me.”