660

660 = 2 x 2 x 3 x 5 x 11.

660 is 1010010100 in base 2 (binary). It is 220110 in base 3 and 22110 in base 4.

660 is the order of a non-cyclic simple group.

660 is the sum of four consecutive primes: 660 = 157 + 163 + 167 + 173. It is also the sum of six consecutive primes: 660 = 101 + 103 + 107 + 109 + 113 + 127. And the sum of eight consecutive primes: 660 = 67 + 71 + 73 + 79 + 83 + 89 + 97 + 101.

660 is the number of feet in a furlong.

Source: What's Special About This Number?