A227627 - OEIS

A227627

Numbers k such that F(5*k)/(5*F(k)) is prime, where F(m) is the m-th Fibonacci number.

2, 3, 5, 7, 13, 25, 29, 37, 47, 67, 457, 2309, 2383, 4133, 5023, 8059

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OFFSET

1,1

COMMENTS

Except for k = 25, all other terms k are primes. Conjecture: this sequence is infinite. - Thomas Ordowski, Jul 18 2013

a(17) > 50000. - Michael S. Branicky, Nov 06 2024

LINKS

MATHEMATICA

Select[Range[1000], PrimeQ[Fibonacci[5*#]/Fibonacci[#]/5]&]

PROG

(PARI) is(n)=ispseudoprime(fibonacci(5*n)/fibonacci(n)/5) \\ Charles R Greathouse IV, Nov 25 2014

CROSSREFS

KEYWORD

nonn,more,hard,changed

AUTHOR

STATUS

approved