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.
"Right now, PBL is still kind of a cool way to address standards and, too often these days, is simply coverage by another name. But its ultimate benefit is to help students think, learn, and operate in the new century by challenging them at deeper levels."