A200921 - OEIS

A200921

Least k such that (3^n + k)*3^n - 1 is a prime number.

1, 1, 3, 3, 13, 9, 15, 3, 1, 13, 29, 1, 5, 53, 25, 9, 23, 1, 69, 13, 3, 3, 17, 1, 5, 117, 5, 13, 45, 51, 3, 11, 31, 73, 49, 43, 11, 83, 93, 277, 171, 383, 39, 11, 3, 31, 55, 61, 61, 13, 73, 107, 65, 137, 53, 39, 467, 53, 233, 277, 17, 53, 109, 177, 151, 97, 13

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OFFSET

1,3

LINKS

Table of n, a(n) for n=1..67.

MATHEMATICA

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

lk[n_]:=Module[{c=3^n, k=0}, While[!PrimeQ[(c+k)c-1], k++]; k]; Array[lk, 70] (* Harvey P. Dale, Aug 19 2015 *)

CROSSREFS

Cf. A191617, A191618, A191619, A191620, A200920, A200922, A200923.

Sequence in context: A020550 A368960 A306529 * A135949 A168234 A141245

Adjacent sequences: A200918 A200919 A200920 * A200922 A200923 A200924

KEYWORD

nonn

AUTHOR

Michel Lagneau, Nov 24 2011

STATUS

approved