From “Man recites pi from memory to 83,431 places“:

A Japanese psychiatric counselor has recited pi to 83,431 decimal places from memory, breaking his own personal best of 54,000 digits and setting an unofficial world record, a media report said Saturday.

Akira Haraguchi, 59, had begun his attempt to recall the value of pi – a mathematical value that has an infinite number of decimal places – at a public hall in Chiba city, east of Tokyo, on Friday morning and appeared to give up by noon after only reaching 16,000 decimal places, the Tokyo Shimbun said on its Web site.

But a determined Haraguchi started anew and had broken his old record on Friday evening, about 11 hours after first sitting down to his task, the paper said. …

Pi, usually given as an abbreviated 3.14, is the ratio of the circumference to the diameter of a circle. The number has fascinated and confounded mathematicians for centuries.

Aided by a supercomputer, a University of Tokyo mathematician set the world record for figuring out pi to 1.24 trillion decimal places in 2002.