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A200923 Least k such that (3^n - k)*3^n + 1 is a prime number. 5
1, 1, 7, 1, 3, 1, 7, 5, 9, 29, 19, 1, 7, 49, 49, 9, 23, 1, 3, 29, 53, 39, 41, 35, 7, 5, 51, 33, 3, 81, 83, 15, 21, 31, 61, 69, 67, 87, 27, 5, 19, 55, 153, 35, 99, 31, 23, 49, 47, 95, 3, 115, 89, 55, 23, 61, 139, 49, 87, 5, 153, 87, 269, 113, 67, 207, 41, 33 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,3

LINKS

Table of n, a(n) for n=1..68.

MATHEMATICA

Table[k = 0; While[!PrimeQ[(3^n - k)*3^n + 1], k++]; k, {n, 72}]

lk[n_]:=Module[{c=3^n, k=1}, While[!PrimeQ[(c-k)*c+1], k++]; k]; Array[lk, 70] (* Harvey P. Dale, Jul 15 2017 *)

CROSSREFS

Cf. A191617, A191618, A191619, A191620, A200920, A200921, A200922.

Sequence in context: A286912 A239807 A130875 * A317830 A317938 A317834

Adjacent sequences:  A200920 A200921 A200922 * A200924 A200925 A200926

KEYWORD

nonn

AUTHOR

Michel Lagneau, Nov 24 2011

STATUS

approved

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Last modified May 9 20:59 EDT 2021. Contains 343746 sequences. (Running on oeis4.)