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A134787
Numbers k such that Fibonacci(prime(k)) is not prime.
21
1, 8, 11, 12, 13, 16, 17, 18, 19, 20, 21, 22, 24, 25, 26, 27, 28, 29, 30, 31, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63, 64, 65, 66, 67, 68, 69, 70, 71, 73, 74, 75, 76, 77, 78, 79, 80, 81, 82, 85, 86
OFFSET
1,2
LINKS
FORMULA
a(n) = pi(A090819(n)). - Amiram Eldar, Oct 25 2024
MATHEMATICA
k = {}; Do[If[ ! PrimeQ[Fibonacci[Prime[n]]], AppendTo[k, n]], {n, 1, 100}]; k
Select[Range[90], !PrimeQ[Fibonacci[Prime[#]]]&] (* Harvey P. Dale, Oct 16 2016 *)
PROG
(Magma) [n: n in [1..100]| not IsPrime(Fibonacci(NthPrime(n)))]; // Vincenzo Librandi, Jan 18 2013
(PARI) is(n)=!isprime(fibonacci(prime(n))) \\ Charles R Greathouse IV, Feb 03 2014
CROSSREFS
Cf. A000720 (pi), A050937, A090819.
Sequence in context: A347313 A077060 A123939 * A249104 A191887 A122195
KEYWORD
nonn,easy,changed
AUTHOR
Artur Jasinski, Nov 12 2007
EXTENSIONS
Definition corrected by N. J. A. Sloane, Nov 12 2007
STATUS
approved