A076646 Numbers n such that sigma(n) * antisigma(n) is a perfect square, where antisigma(n) = sum of the non-divisors of n that are between 1 and n.

1, 2, 15, 20, 24, 28, 104, 224, 5065, 766192670

Offset

1,2

Links

Table of n, a(n) for n=1..10.

Example

sigma(15) * antisigma(15) = 24 * 96 = 48^2, so 15 is a term of the sequence.

Mathematica

l = {}; Do[s = DivisorSigma[1, n]; a = (n (n + 1)/2) - s; If[IntegerQ[Sqrt[a*s]], l = Append[l, n]], {n, 1, 10^5}]; l

Crossrefs

Sequence in context: A042685 A031022 A194542 * A076617 A091791 A281660

Adjacent sequences: A076643 A076644 A076645 * A076647 A076648 A076649

Keyword

nonn

Author

Joseph L. Pe, Oct 23 2002

Extensions

a(10) from Donovan Johnson, Jan 18 2012

Status

approved