8128

8128 = 2 x 2 x 2 x 2 x 2 x 2 x 127.

8128 is a perfect number (2^{7 - 1}(2⁷ - 1)), associated with the Mersenne prime 127 = 2⁷ - 1 (A000396). It is the largest perfect number whose index (4) is equal to the number of digits.

8128 is the 127th triangular number; it is the sum of the first 127 integers. 8128 is the 64th hexagonal number. It is also a centered nonagonal number (A060544).

8128 divides 63¹⁴ - 1.

Source: Number Gossip