Semiperfect number
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In mathematics, a semiperfect number or pseudoperfect number is a natural number n that is equal to the sum of all or some of its proper divisors.
The first few semiperfect numbers are 6, 12, 18, 20, 24, 28, 30, 36, 40, ... Template:OEIS; every multiple of a semiperfect number is semiperfect, and every number of the form 2mp for a natural number m and a prime number p such that 2m < p < 2m + 1 is also semiperfect.
A semiperfect number that is equal to the sum of all its proper divisors is called a perfect number; an abundant number which is not semiperfect is called a weird number.
See also
External link
- MathWorld: Semiperfect number (http://mathworld.wolfram.com/SemiperfectNumber.html)fr:Nombre semi-parfait