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A078178 Least k>=2 such that n^k + n - 1 is prime. 3
2, 2, 2, 2, 2, 3, 2, 2, 2, 2, 4, 2, 16, 2, 2, 4, 3, 2, 2, 2, 7, 4, 2, 3, 2, 3, 2, 10, 2, 2, 108, 3, 6, 2, 3, 7, 2, 2, 4, 2, 16, 3, 2, 2, 2, 20, 2, 7, 2, 3, 3, 2, 2, 2, 2, 9, 4, 2, 2, 7, 8, 3, 2, 2, 2, 24, 2, 6, 2, 12, 4, 3, 8, 6, 2, 4, 3, 9, 194, 3, 13, 2, 8, 2, 2, 3, 8, 2, 10, 6, 4, 2, 2, 54, 2, 132, 4, 10, 2 (list; graph; refs; listen; history; text; internal format)
OFFSET

2,1

COMMENTS

n^a(n) + n - 1 = A078179(n).

LINKS

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

EXAMPLE

7^2+7-1=5*11, but 7^3+7-1=349=A000040(70), therefore a(7)=3.

MATHEMATICA

lkp[n_]:=Module[{k=2}, While[!PrimeQ[n^k+n-1], k++]; k]; Array[lkp, 100, 2] (* Harvey P. Dale, May 24 2020 *)

PROG

(Haskell)

a078178 n = head [k | k <- [2..], a010051'' (n ^ k + n - 1) == 1]

-- Reinhard Zumkeller, Jul 16 2014

CROSSREFS

Cf. A076845, A078179.

Cf. A010051.

Sequence in context: A161966 A187188 A183027 * A306396 A105068 A120676

Adjacent sequences:  A078175 A078176 A078177 * A078179 A078180 A078181

KEYWORD

nonn

AUTHOR

Reinhard Zumkeller, Nov 20 2002

EXTENSIONS

More terms from Benoit Cloitre, Nov 20 2002

STATUS

approved

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Last modified May 22 22:13 EDT 2022. Contains 353959 sequences. (Running on oeis4.)