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 A200922 #6 Mar 30 2012 18:36:00
%S A200922 1,1,1,3,7,1,1,13,17,17,7,43,25,3,41,29,57,11,21,1,25,29,17,27,15,7,
%T A200922 11,63,15,237,73,21,43,229,1,1,73,3,253,63,7,179,3,289,97,157,7,59,95,
%U A200922 237,33,47,3,31,43,141,157,63,137,101,387,109,157,27,29,37
%N A200922 Least k such that (3^n - k)*3^n - 1 is a prime number.
%t A200922 Table[k = 0; While[!PrimeQ[(3^n - k)*3^n - 1], k++]; k, {n, 72}]
%Y A200922 Cf. A191617, A191618, A191619, A191620,A200920, A200921, A200923.
%K A200922 nonn
%O A200922 1,4
%A A200922 _Michel Lagneau_, Nov 24 2011