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 A111471 #4 Dec 05 2013 19:57:05 %S A111471 1,9,7,3,29,19,21,121,7,211,207,11,221,347,99,123,303,189,1131,1179, %T A111471 2069,3437,2211,211,3169,1551,3493,7433,6939,1053,1537,9417,4491,1257, %U A111471 19693,9,1653,3329,317,8667,799,1053,5617,6049,1721,24871,2751,737,3303,29079 %N A111471 a(1) = 1; for n>1, a(n) = least k such that concatenation of n copies of k with all previous concatenations gives a prime. %e A111471 199, 199777, 1997773333, 19977733332929292929 are all primes. %Y A111471 Cf. A111472. %K A111471 base,nonn %O A111471 1,2 %A A111471 _Amarnath Murthy_, Aug 05 2005 %E A111471 More terms from _Donovan Johnson_, Feb 26 2008