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A200921 Least k such that (3^n + k)*3^n - 1 is a prime number. 5
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 (list; graph; refs; listen; history; text; internal format)
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: A206704 A020550 A306529 * A135949 A168234 A141245

Adjacent sequences:  A200918 A200919 A200920 * A200922 A200923 A200924

KEYWORD

nonn

AUTHOR

Michel Lagneau, Nov 24 2011

STATUS

approved

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Last modified June 22 12:56 EDT 2021. Contains 345380 sequences. (Running on oeis4.)