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A067261
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Numbers n such that sigma(n+1)=3*phi(n).
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4
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1, 4, 5, 9, 10, 21, 32, 34, 45, 55, 65, 68, 70, 129, 153, 160, 176, 183, 203, 245, 340, 370, 407, 441, 550, 580, 635, 741, 765, 806, 845, 965, 1011, 1025, 1089, 1166, 1247, 1292, 1505, 1508, 1840, 2271, 2402, 2584, 2590, 3285, 3604, 4065, 4223, 4832, 5339
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OFFSET
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1,2
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LINKS
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MAPLE
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select(n -> numtheory:-sigma(n+1)=3*numtheory:-phi(n), [$1..10000]); # Robert Israel, May 29 2018
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MATHEMATICA
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Select[Range[6000], DivisorSigma[1, #+1]==3*EulerPhi[#]&] (* Harvey P. Dale, Jun 11 2017 *)
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PROG
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(PARI) isok(n) = sigma(n+1) == 3*eulerphi(n); \\ Michel Marcus, May 29 2018
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CROSSREFS
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KEYWORD
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nonn
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AUTHOR
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STATUS
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approved
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