72

72 = 2³ x 3².

72 is the sum of the first eight even numbers: 72 = 2 + 4 + 6 + 8 + 10 + 12 + 14 + 16.

72 is the sum of nine consecutive integers: 72 = 4 + 5 + 6 + 7 + 8 + 9 + 10 + 11 + 12.

72 has a representation as a sum of two squares: 72 = 6² + 6².

72 is 2200 in base 3, 200 in base 6, 110 in base 8, 66 in base 11, 44 in base 17, 33 in base 23, and 22 in base 35.

The normal human pulse rate is about 72 beats per second at rest.

The Cambodian alphabet, with 72 letters, is the longest in the world.

Source: Phillips, R. 2004. Numbers: Facts, Figures and Fiction. Badsey Publications.