678

678 = 2 x 3 x 113. It is the product of three distinct Sophie Germain primes (A157346).

678 is a member of the Fibonacci-like sequence starting with 1 and 7 (A022097).

The sum of the squares of the first 678 primes is a prime (A098561).

678 is the sum of eight positive fifth powers (A003353): 678 = 3⁵ + 3⁵ + 2⁵ + 2⁵ + 2⁵ + 2⁵ + 2⁵ + 2⁵.

678 and the 678th prime (5077) have only the digit 7 in common (A107938).

Source: What's Special About This Number?