A250200 - OEIS

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A250200

Least number k>1 such that (2n-1)^k - 2 is prime, or 0 if no such number exists.

0, 2, 2, 2, 2, 4, 2, 2, 6, 2, 2, 24, 7, 2, 2, 3, 2, 2, 2, 4, 4, 2, 11, 2, 2, 8, 4, 2, 12, 4, 2, 2, 8, 3, 2, 2, 4, 2, 2, 38, 130, 4, 4, 4, 2, 3, 2, 4, 747, 3, 4, 2, 10, 2, 3, 17, 10, 13, 2, 2, 2, 6, 42, 2, 3, 2, 6, 2, 10, 2, 4, 4, 2, 16, 50, 3, 9, 2, 22, 25

(list; graph; refs; listen; history; text; internal format)

OFFSET

1,2

LINKS

Robert Price, Table of n, a(n) for n = 1..143

MATHEMATICA

lst = {0}; For[n = 2, n ≤ 143, n++, For[k = 2, k >= 1, k++, If[PrimeQ[(2*n - 1)^k - 2], AppendTo[lst, k]; Break[]]]]; lst

lnk[n_]:=Module[{k=2, c=2n-1}, While[!PrimeQ[c^k-2], k++]; k]; Join[{0}, Array[ lnk, 80, 2]] (* Harvey P. Dale, Jul 24 2017 *)

CROSSREFS

Cf. A084712, A084713, A084714, A079706, A138066, A255707.

Sequence in context: A349355 A353589 A237709 * A097859 A028326 A156046

Adjacent sequences: A250197 A250198 A250199 * A250201 A250202 A250203

KEYWORD

nonn

AUTHOR

Robert Price, Mar 02 2015

STATUS

approved