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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
OFFSET
1,3
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 *)
KEYWORD
nonn
AUTHOR
Michel Lagneau, Nov 24 2011
STATUS
approved