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A129745 Numbers n such that Lucas(4n)/7 is prime. 0
5, 17, 19, 41, 43, 71, 1511, 2339, 3469, 4787, 7211, 9781 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

L(k) = Lucas(k) = Fibonacci(k-1) + Fibonacci(k+1). 7 = L(4) divides L(4(1+2k)) since L(4n) = L(4)*L(4(n-1)) - L(4(n-2)).

Integer n is in this sequence iff n is prime and 4n belongs to A085726. [From Max Alekseyev, May 16 2010]

LINKS

Table of n, a(n) for n=1..12.

MATHEMATICA

a=7; b=47; Do[ c=7b-a; a=b; b=c; If[ PrimeQ[c/7], Print[n] ], {n, 3, 100}]

CROSSREFS

Cf. A000032, A001606 = Indices of prime Lucas numbers. Cf. A074304 = numbers n such that Lucas(2n)/3 is prime.

Sequence in context: A019349 A226627 A124873 * A304129 A038964 A019401

Adjacent sequences:  A129742 A129743 A129744 * A129746 A129747 A129748

KEYWORD

less,more,nonn

AUTHOR

Alexander Adamchuk, May 14 2007, May 16 2007

EXTENSIONS

a(7) - a(10) from Stefan Steinerberger, May 17 2007

a(11) from Max Alekseyev, Nov 25 2007

a(12) from Alexander Adamchuk, May 15 2010

STATUS

approved

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Last modified January 26 01:48 EST 2020. Contains 331270 sequences. (Running on oeis4.)