A200923 Least k such that (3^n - k)*3^n + 1 is a prime number.

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

Offset: 1

Author

Michel Lagneau, Nov 24 2011

Keywords

• nonn

Crossrefs

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

Programs

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 *)