809

809 is a prime number. It is a Sophie Germain prime because 2 x 809 + 1 = 1619 is also a prime.

809 has a representation as a sum of two squares: 809 = 5² + 28².

809 and 811 form a twin prime pair.

809 is the hypotenuse of a primitive Pythagorean triple: 809² = 280² + 759².

809 is a divisor of 44⁸ - 1.

809 is the only three-digit pime. Pimes are primes whose digits contain circles (that is, use only 0, 6, 8, and 9).

809 was the hotel room number in the 1952 film Don't Bother to Knock, starring Richard Widmark and Marilyn Monroe.

Source: Number Gossip