397

397 is a prime number.

397 is conjectured to be the largest prime that can be represented uniquely as the sum of three positive squares (3² + 8² + 18²).

397 is a Cuban prime. Cuban primes, named after differences between successive cubic numbers, have the form n³ - (n - 1³).

397 has a representation as a sum of two squares: 397 = 6² + 19².

397 is the hypotenuse of a primitive Pythagorean triple: 397² = 228² + 325².

397 Vienna is an asteroid discovered in 1894.

Source: Prime Curios!