"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."
 TECC - The Euler Coding Collective (worldwide)
Just wanted to drop a note (for those who haven't yet read about it via twitter, specifically) that us weird Europeans (at the Metalab, that is) just started a new team called TECC (as in: The Euler Coding Collective), that made it our business to go through every single mathematical problem on the Project Euler site in various languages.
TECC Vienna meets once a week (officially; in fact, it's been a little more often for now) to nerd around together, try out new things and get and give help from/to each other. (Pro tip: running your program while taking the time makes it just so much more a challenge. =)
All in all, I can only most warmly recommend to join the fun! Get your hands on http://projecteuler.net! Let's share our experience and create a pool for all the solutions we found!
Take care, astera
 Git Repository of the Problems we solved (so far):
Watch or download from http://github.com/Metalab/tecc or if you have git installed just:
git clone git://github.com/Metalab/tecc.git
Since not everyone's working on the same Euler problem at the same time, the idea is for each participant to create a subfolder in /tecc named after himself, as in:
Ok, this doesn't yet work so well... so most of the code is still sitting in our mailbox at tecc (at) hackerspaces.org - this should definitely be changed though!!!
Get started, and enjoy! ^^
 The Euler Coders, collected (so far):
|citizen428||ruby, haskell, scala|
|fabian||scala, objective C (someday...)|
|niel||C++, C#, T-SQL, Assembler|