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

Offset: 1

Author

Michel Lagneau, Nov 24 2011

Keywords

• nonn

Crossrefs

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

Programs

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 *)