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 A250297 #12 Jun 08 2015 02:24:51 %S A250297 3,4,7,13,25,34,37,97 %N A250297 Number n such that the n-th term of "concatenate next digit at right hand end (where the next digit after 9 is again 1)" is a semiprime. %C A250297 First unknown: 361. %e A250297 a(4) = 13 so 1234567891234 = 2 * 617283945617 is a semiprime. %Y A250297 Cf. A057137. %K A250297 nonn,base %O A250297 1,1 %A A250297 _Eric Chen_, Dec 26 2014