I’m addicted to ProjectEuler.net … you solve math problems by any means possible, then you will have access to the problem’s forum thread where users share insight on the problems and some even post code (some are Assembly Language wizards that solve a complicated problem in just a few CPU instructions).
The site describes itself as:
Project Euler is a series of challenging mathematical/computer programming problems that will require more than just mathematical insights to solve. Although mathematics will help you arrive at elegant and efficient methods, the use of a computer and programming skills will be required to solve most problems.
I use several tools to solve the problem