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 A111475 #4 Dec 05 2013 19:57:05 %S A111475 7,3,1,1,1,1,129,123,97,559,781,459,253,183,413,417,657,77,437,1439, %T A111475 667,1281,3379,979,2763,1953,103,10083,5103,291,1311,2199,1159,501, %U A111475 5931,483,6171,16301,1781,1229,9519,607,5113,2641,1441,8511,9023,363,4001,15261 %N A111475 a(1) = 7, a(n) = least k such that concatenation of n copies of k with all previous concatenation gives a prime. %e A111475 7,733,733111,... are all prime. %e A111475 733111 = one copy of 7, two copies of 3, three copies of 1. %Y A111475 Cf. A111471, A111472, A111473, A111474, A111476. %K A111475 base,hard,nonn %O A111475 1,1 %A A111475 _Amarnath Murthy_, Aug 05 2005 %E A111475 Extended by _Max Alekseyev_, May 19 2009