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A271430 Values of k such that L(k)*L(k+1)-1 is a prime, where L(k) is the k-th Lucas number (A000032). 1
1, 2, 5, 6, 8, 17, 18, 20, 26, 30, 45, 56, 156, 176, 306, 308, 548, 680, 1197, 2393, 2396, 3870, 4397, 7224, 9734, 17724, 25584, 31793, 44924, 70028, 79760, 91544, 96600 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

a(34) > 10^5. - Robert Price, Apr 17 2016

LINKS

Table of n, a(n) for n=1..33.

EXAMPLE

2 is in the sequence because L(2)*L(3)-1 = 3*4-1 = 11, which is prime.

MATHEMATICA

Select[Range@ 5000, PrimeQ[LucasL@ # LucasL[# + 1] - 1] &] (* Michael De Vlieger, Apr 07 2016 *)

PROG

(PARI)

lucas(n) = fibonacci(n+1) + fibonacci(n-1)

L=List(); for(k=1, 1000, if(ispseudoprime(lucas(k)*lucas(k+1)-1), listput(L, k))); Vec(L)

CROSSREFS

Cf. A000032, A271429.

Sequence in context: A079256 A191204 A191140 * A097685 A136369 A269472

Adjacent sequences:  A271427 A271428 A271429 * A271431 A271432 A271433

KEYWORD

nonn,more

AUTHOR

Colin Barker, Apr 07 2016

EXTENSIONS

a(22)-a(33) from Robert Price, Apr 17 2016

STATUS

approved

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Last modified February 20 14:53 EST 2018. Contains 299380 sequences. (Running on oeis4.)