257

257 is a prime number. It is the second largest known Fermat prime.

257 is 100000001 in base 2 (binary).

257 has a representation as a sum of two squares: 257 = 1² + 16².

257 is the hypotenuse of a primitive Pythagorean triple: 257² = 32² + 255².

There are 257 topologically distinct polyhedral graphs of eight nodes.

257 is the smallest three-digit prime with distinct prime digits.

257 Silesia is an asteroid discovered in 1886.

Source: Number Gossip