In mathematics, a quasiperfect number is a natural number n for which the sum of all its divisors (the divisor function σ(n)) is equal to 2n + 1. Quasiperfect numbers are abundant numbers. No quasiperfect numbers have been found so far, but it has been shown that if any quasiperfect numbers exist, they must be greater than 10³⁵ and have at least seven divisors.

Also see

• Perfect number
• Abundant number
• Deficient number