A078178 - OEIS

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A078178

Least k>=2 such that n^k + n - 1 is prime.

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: A358618 A183027 A359227 * A306396 A355035 A105068` `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 December 28 19:31 EST 2022. Contains 359109 sequences. (Running on oeis4.)