I’m totally hooked on a website called Project Euler. It’s a site with tons of math problems that can be stated simply but generally require a computer to solve. The idea is to help people build both math and programming skills, so it’s a great way to learn things or just practice your chops.
The problems are things like, “Find the sum of all the even-valued terms in the Fibonacci sequence which do not exceed four million.” As the problems get harder, they require you to think of more and more clever solutions — any program you write should be able to run in about a minute, so brute-force solutions don’t always work. So far I’ve found this to be true (although I had one program that took 10 hours to complete… I didn’t figure out a trick for that one). And once you solve a problem, you gain access to a forum for everyone who has solved that problem to share their solutions!
This site’s been around for a while (since 2001), so there are over 230 problems to solve. There are also “levels” — today I finished my 25th problem, finally attaining Level 1:
Anyway, if you like some good ol’ fashioned nerdy fun, I encourage checking it out!