Pi and the square root of two........the just mentioned book said that B. Riemann was trying to calculate the square root of two out to like the 32nd decimal point................

Pi - Wikipedia

https://en.wikipedia.org/wiki/Pi

The number π is a mathematical constant, the ratio of a circle's circumference to its diameter. It is approximately equal to 3.14159. It has been represented by the Greek letter "π" since the mid-18th century, though it is also sometimes spelled out as "pi" (/paɪ/).

‎Letter · ‎Irrational number · ‎Approximations of π · ‎Circumference