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Search: id:A067572
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| A067572 |
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Numbers n such that determinant[{{n, sigma(n)},{n+1, sigma(n+1)}}]is a perfect square. |
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OFFSET
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1,2
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COMMENT
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If n is a term of the sequence, then the parallelogram formed by the vectors {n, sigma(n)},{n+1, sigma(n+1)} has the same area as that of an integral square.
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EXAMPLE
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Det[{{15, sigma(15)},{16, sigma(16)}}] = Det[{{15,24},{16,31}}] = 9^2, so 15 is a term of the sequence.
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MATHEMATICA
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f[n_] := Det[{{n, DivisorSigma[1, n]}, {n + 1, DivisorSigma[1, n + 1]}}]; Do[If[f[n] == 0, Print[n]], {n, 1, 10^6}]
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CROSSREFS
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Sequence in context: A022288 A041432 A072201 this_sequence A066584 A065915 A062965
Adjacent sequences: A067569 A067570 A067571 this_sequence A067573 A067574 A067575
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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), Jan 30 2002
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