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A097605 Numbers n such that phi(n) divides n^2 - 1, where phi(n) (A000010) is number of positive integers <= n and coprime to n. 3
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; text; internal format)
OFFSET

1,2

COMMENTS

All primes are in the sequence. 2 is the only even integer in the sequence.

LINKS

Charles R Greathouse IV, Table of n, a(n) for n = 1..10000

EXAMPLE

phi(35) = 24, 24 divides 35^2 -1 = 1224.

MATHEMATICA

Select[ Range[ 262], Mod[ #^2 - 1, EulerPhi[ # ]] == 0 &] (* Robert G. Wilson v, Sep 01 2004 *)

PROG

(PARI) is(n)=(n^2-1)%eulerphi(n)==0 \\ Charles R Greathouse IV, Feb 21 2013

CROSSREFS

Cf. A098271, A000010.

Sequence in context: A322833 A117287 A121615 * A143578 A187731 A182140

Adjacent sequences:  A097602 A097603 A097604 * A097606 A097607 A097608

KEYWORD

nonn

AUTHOR

Leroy Quet, Aug 30 2004

EXTENSIONS

More terms from Robert G. Wilson v and John W. Layman, Sep 01 2004

STATUS

approved

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Last modified May 22 00:25 EDT 2019. Contains 323472 sequences. (Running on oeis4.)