OFFSET
1,1
COMMENTS
No terms 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
KEYWORD
nonn
AUTHOR
Eric Rowland, May 01 2004
EXTENSIONS
Offset corrected by Giovanni Resta, Jul 20 2013
STATUS
approved