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Search: id:A076646
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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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+0
1
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OFFSET
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1,2
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EXAMPLE
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sigma(15) * antisigma(15) = 24 * 96 = 48^2, so 15 is a term of the sequence.
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MATHEMATICA
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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
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Sequence in context: A041289 A042685 A031022 this_sequence A076617 A091791 A143660
Adjacent sequences: A076643 A076644 A076645 this_sequence A076647 A076648 A076649
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KEYWORD
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nonn
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AUTHOR
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Joseph L. Pe (joseph_l_pe(AT)hotmail.com), Oct 23 2002
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