This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A200920 #6 Mar 30 2012 18:36:00
%S A200920 1,3,1,5,3,25,11,5,13,13,9,7,3,9,17,7,29,25,71,49,7,9,7,9,11,39,7,25,
%T A200920 107,3,67,59,49,89,67,29,113,5,33,7,19,53,3,5,47,121,39,7,407,25,7,
%U A200920 215,29,23,89,5,33,25,113,45,49,109,53,17,109,311,91,145,43
%N A200920 Least k such that (3^n+ k)*3^n + 1 is a prime number.
%t A200920 Table[k = 0; While[!PrimeQ[(3^n + k)*3^n + 1], k++]; k, {n, 72}]
%Y A200920 Cf. A191617, A191618, A191619, A191620, A200921, A200922, A200923.
%K A200920 nonn
%O A200920 1,2
%A A200920 _Michel Lagneau_, Nov 24 2011