What is your favorite number? For many people, it may be an irrational number such as pi (π), Euler’s number (e) or the square root of 2. Even among the natural numbers (positive integers), there are ...

Ah, Friday the 13th. A day of superstition, bad luck and careful avoidance of black cats and broken mirrors. Well, in some cultures, anyway. Though 13 has a long but foggy history of association with ...