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A076845 Least k>0 such that n^k + n - 1 is prime. 4
1, 1, 1, 2, 1, 1, 2, 1, 1, 2, 1, 2, 16, 1, 1, 4, 3, 1, 2, 1, 1, 4, 1, 3, 2, 1, 2, 10, 1, 1, 108, 3, 1, 2, 1, 1, 2, 2, 1, 2, 1, 3, 2, 1, 2, 20, 2, 1, 2, 1, 1, 2, 1, 1, 2, 1, 4, 2, 2, 7, 8, 3, 1, 2, 1, 24, 2, 1, 1, 12, 4, 3, 8, 1, 1, 4, 3, 1, 194, 3, 1, 2, 1, 2, 2, 1, 8, 2, 1, 1, 4, 2, 2, 54, 1, 1, 4, 1, 1 (list; graph; refs; listen; history; text; internal format)
OFFSET

2,4

LINKS

Table of n, a(n) for n=2..100.

MATHEMATICA

lk[n_]:=Module[{k=1}, While[!PrimeQ[n^k+n-1], k++]; k]; Array[lk, 100, 2] (* Harvey P. Dale, Jun 29 2017 *)

PROG

(PARI) a(n) = {my(k=1); while(!isprime(n^k+n-1), k++); k; } \\ Michel Marcus, Nov 29 2013

(Haskell)

a076845 n = head [k | k <- [1..], a010051'' (n ^ k + n - 1) == 1]

-- Reinhard Zumkeller, Jul 17 2014

CROSSREFS

Cf. A078178, A076846.

Cf. A010051.

Sequence in context: A111178 A279187 A254434 * A161906 A204901 A016014

Adjacent sequences:  A076842 A076843 A076844 * A076846 A076847 A076848

KEYWORD

nonn

AUTHOR

Benoit Cloitre, Nov 20 2002

STATUS

approved

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Last modified October 21 19:58 EDT 2019. Contains 328315 sequences. (Running on oeis4.)