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A250200 Least number k>1 such that (2n-1)^k - 2 is prime, or 0 if no such number exists. 3
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: A187467 A081755 A237709 * A097859 A028326 A156046

Adjacent sequences:  A250197 A250198 A250199 * A250201 A250202 A250203

KEYWORD

nonn

AUTHOR

Robert Price, Mar 02 2015

STATUS

approved

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Last modified January 21 06:14 EST 2021. Contains 340333 sequences. (Running on oeis4.)