amicable number
noun
Definitions
One of a pair of numbers having the property that the sum of the divisors of each, excluding itself, is equal to the other number.
Example: The factors of 220, excluding 220 itself, are 1, 2, 4, 5, 10, 11, 20, 22, 44, 55 and 110 and sum to 284; the factors of 284, excluding 284 itself, are 1, 2, 4, 71, and 142, and sum to 220; hence 220 and 284 are amicable numbers.