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Related to perfect number: Amicable number
A positive integer that is equal to the sum of its positive integral factors, including 1 but excluding itself.
(Mathematics) an integer, such as 28, that is equal to the sum of all its possible factors, excluding itself
a positive number that is equal to the sum of all positive integers that are submultiples of it, as 6, which is equal to the sum of 1, 2, and 3.
A positive integer that equals the sum of all of its divisors other than itself. An example is 28, whose divisors (not counting itself) are 1, 2, 4, 7, and 14, which added together give 28.