280

280 = 2 x 2 x 2 x 5 x 7.

280 is 100011000 in base 2 (binary).

280 has a unique representation as a sum of three squares: 280 = 6² + 10² + 12².

The sum of the first 280 consecutive primes mod 280 is prime.

280 is the number of ways 18 people around a round table can shake hands in a non-crossing way, up to rotation.

280 is an octagonal number.

Source: Prime Curios!