Project Euler is a website that proposes various problems, related to programming and/or math. You can solve the problem anyway you like, as it only asks for the result. If you get it right, you can then check out how others have done it or, in some cases, have an explanation from the guys at project euler.
It is very addictive and fun, I highly recommend it!
I've been solving the problems entirely in Ruby, and committing my code to github. Check out my solutions, and don't hesitate to let me know if you find a better one, or even a bug. ;)
