Almost perfect number
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 2
n - 1. The only almost perfect numbers known are those of the form 2
k 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.
Also see
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