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?

The number 1 is not considered a prime number because it has only 1 positive divisor. Some prime numbers form “twin primes,” like 11 and 13 or 17 and 19. These pairs differ by exactly two. Large prime ...

Find one million consecutive positive numbers, none of which are prime. Ancient math tells us that prime numbers (2, 3, 5, 7, 11, ...,), which have no factors except for 1 and themselves, go on ...

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 ...