6680

6680 = 2 x 2 x 2 x 5 x 167.

6680 = 6666 + 6 + 8 + 0.

6680 is the number of essentially different ways in which the squares 1, 4, 9, . . . 16² can be arranged in a sequence such that all pairs of adjacent squares sum to a prime number (rotations and reversals are counted only once) (A073451).

6680 and the square of 6680 (44622400) use only the digits 0, 2, 4, 6, and 8 (A136904).

6680 is a number n such that n², n² + 1, and n² + 2 are all semiprimes (A179502).

Source: What's Special About This Number?