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A015715
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Odd integers m such that phi(m) | sigma(m).
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2
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1, 3, 15, 35, 105, 357, 1045, 1485, 3135, 3339, 5049, 10659, 12441, 16065, 24871, 24969, 29029, 33915, 35343, 39105, 39585, 50065, 58435, 64285, 71145, 74613, 87087, 87685, 99693, 124355, 124605, 132957, 137885, 140335, 145145, 150195
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OFFSET
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1,2
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COMMENTS
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Subsequence of A236693. Proof: if n is in this sequence, then 2^phi(n) - 1 is divisible by n and 2^sigma(n) - 1 is divisible by 2^phi(n) - 1. Therefore, 2^sigma(n) == 1 (mod n) and n is in A236693. - Jinyuan Wang, Mar 13 2020
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LINKS
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Donovan Johnson, Table of n, a(n) for n = 1..1000
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MATHEMATICA
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Select[Range[1, 151001, 2], Divisible[DivisorSigma[1, #], EulerPhi[#]]&] (* Harvey P. Dale, Sep 16 2016 *)
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PROG
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(PARI) isok(m) = (m % 2) && !(sigma(m) % eulerphi(m)); \\ Michel Marcus, Mar 14 2020
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CROSSREFS
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Cf. A000010, A000203, A020492, A236693.
Sequence in context: A145949 A015809 A293995 * A187787 A290717 A019009
Adjacent sequences: A015712 A015713 A015714 * A015716 A015717 A015718
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KEYWORD
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nonn
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AUTHOR
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Robert G. Wilson v
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EXTENSIONS
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Offset corrected by Donovan Johnson, Jan 18 2012
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STATUS
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approved
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