π - pi
Mnemonic
How I want a drink alcholic of course after all those lectures involving quantum mechanics.
3.1415 926 5358 979 ...
A common approximation for π is 22/7, the Great pyramid is build with ratio 440/140. Zu Chongzhi found algebraic series to calculate π to arbitrary precision, in China the ratio 355/113 is a common approximation.