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A015722
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Odd composite n such that phi(n) * sigma(n) is one less than a square.
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3
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33, 69, 295, 423, 451, 531, 581, 1119, 2893, 4043, 4163, 4257, 4509, 5975, 12977, 14927, 15753, 19105, 25369, 27225, 38013, 38799, 39771, 85675, 98531, 157375, 217349, 264439, 324643, 330977, 352593, 382881, 417661
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OFFSET
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1,1
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LINKS
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MATHEMATICA
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nn=420000; okQ[n_]:=IntegerQ[Sqrt[EulerPhi[n]DivisorSigma[1, n]+1]]; Select[Complement[Range[1, nn, 2], Prime[Range[PrimePi[nn]]]], okQ] (* Harvey P. Dale, Mar 27 2011 *)
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PROG
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CROSSREFS
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KEYWORD
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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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