Almost perfect number
From Wikipedia, the free encyclopedia
In mathematics, an almost perfect number (sometimes also called slightly defective number) is a natural number n such that the sum of all divisors of n (the divisor function σ(n)) is equal to 2n - 1. The only almost perfect numbers known are those of the form 2k for some natural number k; however, it has not been shown yet that all almost perfect numbers are of this form. Almost perfect numbers are deficient numbers.
[edit] See also
- Semiperfect number
- Quasiperfect number
- Perfect number
- Multiply perfect number
- Hyperperfect number
- Unitary perfect number
- Abundant number
