Pi Day 2015: a sweet treat for maths fans

Ratio of a circle's circumference to its diameter has sparked memory contests and even a language - this year's celebration of I is a once-in-100-year occasion

He ate all the pi : Japanese man memorises I to 111,700 digits

A date falls on this Saturday that only comes once every 100 years - and geeks around the world are very excited.

It's Pi Day, the celebration date of the number that is the ratio of a circle's circumference to its diameter. The celebration is held annually on 14 March, because 3/14 spells out the first three digits of I, or pi, which is 3.14.