The following formula for π was discovered by Ramanujan:
Does anyone know how it works, or what the motivation for it is?
Here’s an easy introduction to the basics, “Pi Formulas and the Monster Group“.
Update: Just to make this more intriguing, define the fundamental unit U29=5+√292 and fundamental solutions to Pell equations,
then we can see those integers all over the formula as,
See also this MO post.