Whole number for which the sum of its proper divisors is equal to the number itself.

### Examples

- Consider the number 496.

The sum of its proper divisors is 496, because: 1 + 2 + 4 + 8 + 16 + 31 + 62 + 124 + 248 = 496.

Therefore, 496 is a perfect number. - Consider the whole number 20.

The sum of its proper divisors is 22, because: 1 + 2 + 4 + 5 + 10 = 22.

Because 22 > 20, 22 is an abundant number. - Consider the number 81.

The sum of its proper divisors is 40 because: 1 + 3 + 9 + 27 = 40.

Because 40 < 81, 81 is a deficient number. - The numbers 6 and 28 are also perfect numbers.