- U.S.A. Mathematical Olympiad
- International Mathematics Olympiad (IMO)
- Bertrand's Paradox
*(a discovery that made mathematicians wary of the whole notion of probability)* - Mathematical Games and Recreations (History of Mathematics archive-U St Andrews)
- Recreational Mathematics (David Eppstein-UC Irvine)
- Eisenhower National Clearinghouse (ENC) Online (K-12 Math Resources)