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A076646
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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.
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OFFSET
| 1,2
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EXAMPLE
| sigma(15) * antisigma(15) = 24 * 96 = 48^2, so 15 is a term of the sequence.
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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
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CROSSREFS
| Sequence in context: A042685 A031022 A194542 * A076617 A091791 A143660
Adjacent sequences: A076643 A076644 A076645 * A076647 A076648 A076649
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KEYWORD
| nonn
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AUTHOR
| Joseph L. Pe (joseph_l_pe(AT)hotmail.com), Oct 23 2002
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EXTENSIONS
| a(10) from Donovan Johnson (donovan.johnson(AT)yahoo.com), Jan 18 2012
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