1800

1800 = 2 x 2 x 2 x 3 x 3 x 5 x 5.

1800 is a pentagonal pyramidal number.

1800 is the sum of 10 consecutive primes: 1800 = 157 + 163 + 167 + 173 + 179 + 181 + 191 + 193 + 197 + 199.

1800 is 5151 in base 7. It is 800 in base 15.

1800 has two representations as a sum of two squares: 1800 = 6² + 42² = 30² + 30².

1800 divides 49⁶ - 1.

Source: Prime Curios!