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 A135475 #10 Mar 30 2012 16:50:47 %S A135475 123,1123,1223,1233,11123,11223,11233,12123,12223,12233,12323,12333, %T A135475 111123,111223,111233,112123,112223,112233,112323,112333,121123, %U A135475 121223,121233,122123,122223,122233,122323,122333,123123,123223,123233,123323,123333,1111123 %N A135475 Sorted list of strings that can be obtained by starting with 123 and repeatedly doubling any substring in place. %C A135475 The list contains A135473(n) strings of length n. %H A135475 Alois P. Heinz, <a href="/A135475/b135475.txt">Table of n, a(n) for n = 1..10397</a> (strings with length <= 12) %H A135475 <a href="/index/Do#repeat">Index entries for doubling substrings</a> %Y A135475 Cf. A135473, A130838, A135479, A135017. %K A135475 nonn,easy %O A135475 1,1 %A A135475 _N. J. A. Sloane_, Feb 22 2008, Mar 16 2008