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 A111477 #7 Dec 05 2013 19:57:05 %S A111477 11,19,19,37,21,71,101,39,61,87,227,63,437,153,1363,117,363,861,609, %T A111477 249,23,1077,3123,771,3717,633,279,1119,927,107,3843,4313,1729,627, %U A111477 12541,2403,4083,1239,2227,6441,3819,3983,5631,2303,2971,19217,3633,5109,14413,913 %N A111477 a(1) = 11, a(n) = least k such that concatenation of n copies of k with all previous concatenation gives a prime. %e A111477 11,111919,111919191919,... are all prime. %e A111477 111919191919 = one copy of 11, two copies of 19, three copies of 19. %Y A111477 Cf. A111471, A111472, A111473, A111474, A111475, A111478. %K A111477 base,nonn %O A111477 1,1 %A A111477 _Amarnath Murthy_, Aug 05 2005 %E A111477 a(4)-a(8) from _Stefan Steinerberger_, Nov 17 2005 %E A111477 Extended by _Max Alekseyev_, May 20 2009