semiperfect number

English

Noun

Examples
18 is a semiperfect number because its proper divisors are 1, 2, 3, 6, and 9, and adding together e.g. 3 + 6 + 9 = 18. 6 is a semiperfect (and also fully perfect) number because its proper divisors, 1, 2, and 3, sum to itself.

semiperfect number (plural semiperfect numbers)

1. (mathematics) A number which is the sum of some, or all, of its proper divisors.

   Synonym: pseudoperfect number