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A094394 Odd composite n such that n divides Fibonacci(n)-1. 9
323, 2737, 4181, 6479, 6721, 7743, 11663, 13201, 15251, 18407, 19043, 23407, 27071, 34561, 34943, 35207, 39203, 44099, 47519, 51841, 51983, 53663, 54839, 64079, 64681, 65471, 67861, 68251, 72831, 78089, 79547, 82983, 86063, 90061, 94667 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

No entries satisfy the Fermat criterion 2^(a(n)-1) mod a(n) = 1. - Gary Detlefs, May 25 2014

For each prime p, Fibonacci(p) = 5^((p-1)/2) mod p, so p divides Fibonacci(p) - 1 for each prime p=10k+-1. Hence it is interesting to seek also nonprimes with the same property, a motivation for this sequence. - Robert FERREOL, Jul 14 2015

LINKS

Giovanni Resta, Table of n, a(n) for n = 1..1000

MAPLE

with(combinat):test:=n->(fibonacci(n)-1) mod n= 0:

select(test and not isprime , [seq(2*k+1, k=1..10000)]); # Robert FERREOL, Jul 14 2015

MATHEMATICA

Select[Range[2, 50000], OddQ[#] && ! PrimeQ[#] && Mod[Fibonacci[#] - 1, #] == 0 &]

PROG

(PARI) main(m)=forcomposite(n=1, m, if(((n%2==1)&&(fibonacci(n)-1)%n==0), print1(n, ", "))); \\ Anders Hellström, Aug 12 2015

CROSSREFS

Cf. A094395, A094400.

Sequence in context: A065884 A252452 A202610 * A296973 A213289 A094409

Adjacent sequences:  A094391 A094392 A094393 * A094395 A094396 A094397

KEYWORD

nonn

AUTHOR

Eric Rowland, May 01 2004

EXTENSIONS

Offset corrected by Giovanni Resta, Jul 20 2013

STATUS

approved

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Last modified January 18 13:55 EST 2020. Contains 331010 sequences. (Running on oeis4.)