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A097605
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Numbers n such that phi(n) divides n^2 - 1, where phi(n) (A000010) is number of positive integers <= n and coprime to n.
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2
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1, 2, 3, 5, 7, 11, 13, 15, 17, 19, 23, 29, 31, 35, 37, 41, 43, 47, 53, 59, 61, 65, 67, 71, 73, 79, 83, 89, 91, 97, 101, 103, 107, 109, 113, 127, 131, 137, 139, 149, 151, 157, 163, 167, 173, 179, 181, 191, 193, 197, 199, 211, 223, 227, 229, 233, 239, 241, 251, 255, 257
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,2
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COMMENTS
| All primes are in the sequence. 2 is the only even integer in the sequence.
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EXAMPLE
| phi(35) = 24, 24 divides 35^2 -1 = 1224.
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MATHEMATICA
| Select[ Range[ 262], Mod[ #^2 - 1, EulerPhi[ # ]] == 0 &] (from Robert G. Wilson v Sep 01 2004)
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CROSSREFS
| Cf. A098271, A000010.
Sequence in context: A003277 A117287 A121615 * A143578 A187731 A190223
Adjacent sequences: A097602 A097603 A097604 * A097606 A097607 A097608
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KEYWORD
| nonn
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AUTHOR
| Leroy Quet Aug 30 2004
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EXTENSIONS
| More terms from Robert G. Wilson v (rgwv(AT)rgwv.com) and John W. Layman (layman(AT)math.vt.edu), Sep 01 2004
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