One day in January 1913. G. H. Hardy, a famous Cambridge University mathematician received a letter from an Indian named Srinivasa Ramanujan asking him for his opinion of 120 mathematical theorems ( 定理 ) that Ramanujan said he had discovered. To Hardy, many of the theorems made no sense. Of the others, one or two were already well-known. Ramanujan must be some kind of trickplayer, Hardy decided, and put the letter aside. But all that day the letter kept hanging round Hardy. Might there be something in those wild-looking theorems? That evening Hardy invited another brilliant Cambridge mathematician, J. E. Littlewood, and the two men set out to assess the Indian’s worth. That incident was a turning point in the history of mathematics. At the time, Ramanujan was an obscure Madras Port Trust clerk. A little more than a year later, he was at Cambridge University, and beginning to be recognized as one of the most amazing mathematicians the world has ever known. Though he died in 1920, much of his work was so far in advance of his time that only in recent years is it beginning to be properly understood. Indeed, his results are helping solve today’s problems in computer science and physics, problems that he could have had no notion of. For Indians, moreover, Ramanujan has a special significance. Ramanujan, though born in poor and ill-paid accountant’s family 100 years ago, has inspired many Indians to adopt mathematics as career. Much of Ramanujan’s work is in number theory, a branch of mathematics that deals with the subtle ( 难以捉摸的 ) laws and relationships that govern numbers. Mathematicians describe his results as elegant and beautiful but they are much too complex to be appreciated by laymen. His life, though, is full of drama and sorrow. It is one of the great romantic stories of mathematics, a distressing reminder that genius can suce and rise in the most unpromising circumstances.