281

281 is a prime number. It is also a Sophie Germain prime because 2 x 281 + 1 = 563 is prime.

281 has a representation as a sum of two squares: 281 = 5² + 16².

281 and 283 form a twin prime pair.

281 is the hypotenuse of a primitive Pythagorean triple: 281² = 160² + 231².

The final repeated digit-products of consecutive integers 281, 282, and 283 are all 6: 2 x 8 x 1 = 16, 1 x 6 = 6; 2 x 8 x 2 = 32, 3 x 2 = 6; 2 x 8 x 3 = 48, 4 x 8 = 32, 3 x 2 = 6. There are no four consecutive integers with the same final digit-product less than 6 x 24 x 10⁸.

281 is the sum of the first 14 primes (up to 43). If we add consecutive primes up to 281, the total is also a prime (7699). There are no other such primes with this behavior between 281 and 7699.

281 is a telephone area code for Houston, Texas.

Source: The Penguin Dictionary of Curious and Interesting Numbers, rev. ed., by David Wells.