After hearing about it for years, I decided to start working through Project Euler about two weeks ago. It really is much more about math than programming, although it's a lot of fun to take on the problems with a language that has tail call optimization because so many of the problems involve recurrence relations.

I like that the problems are constructed in a way that usually punishes you for trying to use brute force. Sometimes there's a problem that doesn't have a more elegant solution, though, as if to remind us that brute force often works remarkably well.