If you feel a little odd today, your calendar might explain why. Today’s date, 9/11/13, is a mathematical phenomenon so rare that it only occurs five times every 100 years. This is the last time for ...

All of these puzzles relate to adding together consecutive numbers. Mathematicians do not like doing a lot of, tedious adding up, and so are always on the lookout for cunning shortcuts. It might help ...

SAN FRANCISCO – Ron Gordon would like you to take a moment or three to think about what an odd day Saturday is. Why? Because 7/9/11 is one of only six dates this century that features three ...