

A076646


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


0




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



