Akira Haraguchi, of Kisarazu, Chiba Prefecture, is a world-class athlete, and in his particular sport he is the best in the world. You might be puzzled if you saw him: He’s 72, a retired engineer and doesn’t look like a reigning world champion. But his sport is played in the mind, and Haraguchi’s mind is trained to the very highest level. He is a memory athlete.

In 2006, Haraguchi recited the mathematical constant pi to 100,000 digits, in a feat that lasted more than 16 hours. Pi, of course, is the ratio of a circle’s circumference to its diameter, and is an infinite and irrational number. That means it goes on forever, with no repeating patterns of numbers.

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