- Primitive semiperfect number
In

mathematics , a**primitive semiperfect number**(also called a "primitive pseudoperfect number", "irreducible semiperfect number" or "irreducible pseudoperfect number") is a semiperfectnatural number that has no semiperfect properdivisor .The first few primitive semiperfect numbers are 6, 20, 28, 88, 104, 272, 304, 350, ... (sequence [

*http://www.research.att.com/cgi-bin/access.cgi/as/njas/sequences/eisA.cgi?Anum=A006036 A006036*] inOEIS ).There are infinitely many odd primitive semiperfect numbers (the smallest is 945,) as well as infinitely many primitive semiperfect numbers that are not

harmonic divisor number s.**External links*** [

*http://mathworld.wolfram.com/PrimitiveSemiperfectNumber.html MathWorld: Primitive semiperfect number*]

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