I know it’s a bit late, but 22 July (22/7) was Pi Approximation Day.

Piece of pieThe fraction 22/7 is an approximation of pi, the mathematical constant that describes the ratio of a circle’s circumference to its diameter. Pi has an infinite number of non-repeating digits after the decimal point – see this site for the first million digits (or not…) Pi Day is 14 March (3.14), of course!