semiperfect number

A pseudoperfect number, sometimes also called a semiperfect number , is a positive integer such as 20 = 1 + 4 + 5 + 10 which is the sum of some (or all) of its proper divisors. Identifying pseudoperfect numbers is therefore equivalent to solving the subset sum problem. A pseudoperfect number which is the sum of all its proper divisors is called a perfect number. The first few pseudoperfect numbers are 6, 12, 18, 20, 24, 28, 30, 36, 40, ... (OEIS A005835).

abundant number | deficient number | perfect number | primary pseudoperfect number | primitive pseudoperfect number | subset sum problem | weird number