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

1,3

Links

Table of n, a(n) for n=1..68.

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 *)

Crossrefs

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

Sequence in context: A239807 A130875 A370112 * A317830 A317938 A317834

Adjacent sequences: A200920 A200921 A200922 * A200924 A200925 A200926

Keyword

nonn

Author

Michel Lagneau, Nov 24 2011

Status

approved