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A023173 Numbers k such that Fib(k) == 1 (mod k). 12
1, 2, 11, 19, 22, 29, 31, 38, 41, 58, 59, 61, 62, 71, 79, 82, 89, 101, 109, 118, 122, 131, 139, 142, 149, 151, 158, 178, 179, 181, 191, 199, 202, 211, 218, 229, 239, 241, 251, 262, 269, 271, 278, 281, 298, 302, 311, 323, 331, 349, 358, 359, 362, 379, 382, 389, 398, 401 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

Sequence contains 1, A064739(k) for all k>=0, 2*A064739(k) for k>1. - Benoit Cloitre, Apr 06 2002

LINKS

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

MATHEMATICA

lst={}; Do[If[Mod[Fibonacci[n], n]==1, AppendTo[lst, n]], {n, 1, 7!}]; Take[Union[lst], 5! ] (* Vladimir Joseph Stephan Orlovsky, Apr 03 2009 *)

Select[Range[500], Mod[Fibonacci[#]-1, #]==0&] (* Harvey P. Dale, Sep 22 2021 *)

PROG

(PARI) fibmod(n, m)=((Mod([1, 1; 1, 0], m))^n)[1, 2]

is(n)=fibmod(n, n)==1 \\ Charles R Greathouse IV, Oct 06 2016

CROSSREFS

Cf. A045468, A003631, A064739.

Sequence in context: A074926 A066144 A102343 * A018443 A163058 A161504

Adjacent sequences:  A023170 A023171 A023172 * A023174 A023175 A023176

KEYWORD

nonn,easy

AUTHOR

David W. Wilson

STATUS

approved

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Last modified November 27 12:51 EST 2021. Contains 349394 sequences. (Running on oeis4.)