1687

1687 = 7 x 241.

1687, 1689, and 1691 are all semiprimes (A092125), the product of two primes.

1687 is 777 in base 15.

The last 1687 digits of 1687¹⁶⁸⁷ form a prime number.

1687 and its reversal 7861 are both multiples of 7 (A062901).

1687 is the sum of three consecutive hexagonal numbers (A129109): 1687 = 496 + 561 + 630.

Source: Prime Curios!