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A331195 Numbers k such that prime(prime(k)) is a Fibonacci number. 3
1, 2, 54, 445, 8079037, 75526509638399 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

LINKS

Table of n, a(n) for n=1..6.

FORMULA

a(n) = pi(A331345(n)).

a(n) = pi(pi(A329973(n))).

MATHEMATICA

A45 = Fibonacci[Range[40]]; searchMax = PrimePi[PrimePi[A45[[-1]]]]; Select[Range[searchMax], MemberQ[A45, Prime[Prime[#]]] &] (* Alonso del Arte, Jan 11 2020 *)

PROG

(PARI) isfib(k) = my(m=5*k^2); issquare(m-4) || issquare(m+4);

isok(k) = isfib(prime(prime(k))); \\ Michel Marcus, Jan 31 2020

CROSSREFS

Cf. A000040, A000045, A000720, A006450, A099000, A329973, A330966, A331345.

Sequence in context: A078691 A280754 A113028 * A200195 A202739 A055024

Adjacent sequences:  A331191 A331192 A331193 * A331196 A331197 A331198

KEYWORD

nonn,hard,more

AUTHOR

Elizabeth Axoy, Jan 11 2020

STATUS

approved

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Last modified March 28 05:38 EDT 2020. Contains 333073 sequences. (Running on oeis4.)