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Search: id:A056917
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| A056917 |
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Numbers n such that sigma(n)-phi(n) is a perfect square. |
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+0
2
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| 1, 15, 30, 44, 65, 77, 78, 87, 105, 141, 147, 186, 242, 247, 282, 301, 330, 335, 345, 450, 481, 560, 570, 589, 591, 606, 671, 705, 717, 767, 777, 785, 819, 820, 870
(list; graph; listen)
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OFFSET
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1,2
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EXAMPLE
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sigma(44)-phi(44) = 84 - 20 = 8^2, so 44 is a term of the sequence.
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MATHEMATICA
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Select[Range[10^3], IntegerQ[Sqrt[DivisorSigma[1, # ] - EulerPhi[ # ]]] &]
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CROSSREFS
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Sequence in context: A060700 A167210 A131933 this_sequence A044855 A044900 A008597
Adjacent sequences: A056914 A056915 A056916 this_sequence A056918 A056919 A056920
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KEYWORD
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easy,nonn
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AUTHOR
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Joseph L. Pe (joseph_l_pe(AT)hotmail.com), Feb 12 2002
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