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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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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, 1007, 1032, 1056, 1071, 1102, 1167, 1173, 1185, 1230, 1247, 1271, 1351, 1374, 1415, 1416, 1501
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OFFSET
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1,2
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LINKS
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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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PROG
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(PARI) isok(n) = issquare(sigma(n) - eulerphi(n)); \\ Michel Marcus, Oct 19 2016
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CROSSREFS
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KEYWORD
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easy,nonn
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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