An abundant number is a natural number for which the sum of divisors satisfies , or, equivalently, the sum of proper divisors (or aliquot sum) satisfies . The abundance of a natural number is the integer (equivalently, ).

The abundant numbers smaller than 100 are
:12, 18, 20, 24, 30, 36, 40, 42, 48, 54, 56, 60, 66, 70, 72, 78, 80, 84, 88, 90, and 96 .For example, the proper