What does it mean for something to be a sum of squares? Take the number 13. It’s the sum of two squares: 2 2 and 3 2. The number 34 is the sum of 3 2 plus 5 2. Instead of numbers, Hilbert’s ...

If a prime number is the sum of two squares, then it’s not a Gaussian prime. So when you note that 13 = 4+9, and that 89 = 25+64, you’re observing that 13 and 89 are not Gaussian primes.

Which ones can be written as a sum of two squares? Each one is an odd number, so its remainder after dividing by 4 is either 1 or 3, and the result is very simply stated.

If you enjoy Pi Day (3/14) and Avogadro’s Number Day (10/23), then get this: today is a Pythagorean triple date. You’d have to be a serious math nerd to recognize that the sum of the squares ...