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 A201131 #6 Mar 30 2012 18:36:00
%S A201131 3,1,11,1,5,19,9,1,11,15,9,69,27,21,77,85,53,1,5,201,9,43,93,403,45,
%T A201131 87,17,63,45,15,23,9,17,273,51,31,111,277,45,39,51,229,9,109,29,357,
%U A201131 81,1,237,33,137,169,137,847,75,367,57,87,285,25,105,177,113,1
%N A201131 Least k such that (5^n - k)*5^n + 1 is a prime number.
%t A201131 Table[k = 0; While[!PrimeQ[(5^n - k)*5^n + 1], k++]; k, {n, 85}]
%Y A201131 Cf. A200923, A200923.
%K A201131 nonn
%O A201131 1,1
%A A201131 _Michel Lagneau_, Nov 27 2011