Project Euler
quoted from the siteProject 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.
The motivation for starting Project Euler, and its continuation, is to
provide a platform for the inquiring mind to delve into unfamiliar
areas and learn new concepts in a fun and recreational context.
you can find the Problems here:
http://projecteuler.net/index.php?section=problems
its really interesting!!
you can try it yourself ...
using any programming language, you just have to give them the result