Multiply perfect number

In mathematics, a multiply perfect number (also called multiperfect number or pluperfect number) is a generalization of a perfect number.

For a given natural number k, a number n is called k-perfect (or k-fold perfect) iff the sum of all positive divisors of n (the divisor function, σ(n)) is equal to kn; a number is thus perfect iff it is 2-perfect. A number that is k-perfect for a certain k is called a multiply perfect number.

It can be proven that:

• For a given prime number p, if n is p-perfect and p does not divide n, then pn is (p+1)-perfect.
• If 3n is 4k-perfect and 3 does not divide n, then n is 3k-perfect.

Smallest k-perfect numbers

The following table gives an overview of the smallest k-perfect numbers for k <= 7 (cf. Sloane's A007539):

k	Smallest k-perfect number	Found by
2	6	ancient
3	120	ancient
4	30240	René Descartes, circa 1638
5	14182439040	René Descartes, circa 1638
6	154345556085770649600	unknown
7	141310897947438348259849402738485523264343544818565120000	unknown

External links

• The Multiply Perfect Numbers page
• The Prime Glossary: Multiply perfect numbers