509

509 is a prime number. Because 2 x 509 + 1 = 1019 is a prime, 509 is also a Sophie Germain prime.

509 is the sum of three consecutive squares: 12² + 13² + 14² = 509.

In base 4, 509 is the palindrome 13331.

509 has a representation as a sum of two squares: 509 = 5² + 22².

509 is the hypotenuse of a primitive Pythagorean triple: 509² = 220² + 459².


In the Clint Eastwood movie Firefox, 509 is the number on the conning tower of the submarine beneath the icepack.

Source: Prime Curios!