A178250 - OEIS

A178250

Least number x such that n^x-n-1 is prime.

3, 2, 2, 2, 2, 2, 3, 2, 2, 2, 2, 4, 2, 3, 2, 2, 3, 5, 2, 2, 2, 3, 3, 2, 4, 2, 5, 2, 5, 2, 2, 7, 5, 3, 2, 9, 3, 2, 2, 3, 2, 31, 4, 2, 2, 2, 3, 2, 4, 2, 108, 4, 2, 2, 2, 2, 3, 3, 2, 2, 18, 7, 3, 2, 2, 2, 4, 2, 3, 2, 5, 32, 108, 5, 3, 2, 11, 4, 15, 3, 4, 19, 2, 6, 2, 2, 11, 107, 2, 42, 4, 39, 2, 2, 6, 2, 3

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OFFSET

2,1

COMMENTS

Least number x such that x^n-x-1 is prime see A127599.

LINKS

Table of n, a(n) for n=2..98.

MATHEMATICA

a = {}; Do[k = 2; While[ ! PrimeQ[n^k - n - 1], k++ ]; AppendTo[a, k], {n, 2, 500}]; a (*Artur Jasinski*)

lnx[n_]:=Module[{x=1}, While[!PrimeQ[n^x-n-1], x++]; x]; Array[lnx, 100, 2] (* Harvey P. Dale, Jul 09 2017 *)

CROSSREFS

Cf. A127599