681

681 = 3 x 227.

The sum of the digits of 681 is five times the number of digits: 6 + 8 + 1 = 15 = 3 x 5.

681 is the sum of 11 positive 5th powers: 681 = 3⁵ + 3⁵ + 2⁵ + 2⁵ + 2⁵ + 2⁵ + 2⁵ + 2⁵ + 1⁵ + 1⁵ + 1⁵.


681 is a centered pentagonal number.


The galaxy NGC 681, more than 55 million light years away, resembles the striking Sombrero Galaxy (M104).

Source: Wolfram MathWorld