The crisp new dollar bill that I have just taken from my wallet bears the serial number 24598176. It’s easy to tell that the number is exactly divisible by 2 but not by 5. Is it divisible by 3? by 4?

Randomly scramble the digits 0, 1, 2, 3, 4, 5 and 6 to form a seven-digit number (or a six-digit number if the leading digit is 0). Rank the following events in order ...

Three and five are prime numbers - that is, they are divisible only by one and by themselves. So are five and seven. And 11 and 13. And for each of these pairs of prime numbers, the difference is two.

DO you have a preference for odd or even numbers? Marissa Mayer, the CEO of Yahoo, does: “I really like even numbers, and I like heavily divisible numbers,” she says in the latest Vogue. “Twelve is my ...