Definitions for "Perfect number"
Keywords:  divisors, integer, proper, sum, twice
(4) A number in which the sum of all its proper factors is equal to the number itself. Example: 6 is a perfect number because when you add its proper factors the answer is equal to 6: 1 + 2 + 3 = 6.
A number whose proper factors sum up to the number itself. For example, the proper factors of 6 are 1, 2, and 3, which sum to 6.
an integer greater than zero whose factors less than the number all add up to the number (i
a tight little mathematical bundle, self-contained and -referenced