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A015722
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Composite and odd 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
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,1
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REFERENCES
| R. K. Guy, Divisors and desires, Amer. Math. Monthly, 104 (1997), 359-360.
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LINKS
| Donovan Johnson, Table of n, a(n) for n = 1..300
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MATHEMATICA
| nn=420000; okQ[n_]:=IntegerQ[Sqrt[EulerPhi[n]DivisorSigma[1, n]+1]]; Select[Complement[Range[1, nn, 2], Prime[Range[PrimePi[nn]]]], okQ] (* From Harvey P. Dale, Mar 27 2011 *)
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CROSSREFS
| Sequence in context: A055078 A044135 A044516 * A103046 A063868 A184417
Adjacent sequences: A015719 A015720 A015721 * A015723 A015724 A015725
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KEYWORD
| nonn
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AUTHOR
| Robert G. Wilson v (rgwv(AT)rgwv.com)
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EXTENSIONS
| Offset corrected by Donovan Johnson (donovan.johnson(AT)yahoo.com), Jan 16 2012
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