My friend Aaron just pointed me to this site, but I think I’d seen it before, in a less-polished state.
Project Euler (http://projecteuler.net/)
This page has a sequence of 360 challenging math and computing problems. If you sign up for an account, you can track your progress in solving the problems. The problems are not trivial at all, so this looks like a great way to challenge yourself and grow both mathematically and in terms of programming.
I’m curious who set up this site. Even more, I think it would be great to work as a team to solve these problems. Add this to my list of fun things to do, if I only had time…