684

684 = 2 x 2 x 3 x 3 x 19.

684 has the representation 684 = 3⁶ - 45.

684 is the sum of three consecutive cubes (A024975): 684 = 5³ + 6³ + 7³.

684 is 221100 in base 3.

684 is the largest number that is 38 times the sum of its digits (A052489): 684 = 38 x 18.

Halley's Comet was visible from Earth in the year 684.

Source: What's Special About This Number?