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 A159903 #5 Aug 09 2015 15:00:20 %S A159903 4,48,489,48912,4891216,489121618,48912161820,4891216182024, %T A159903 489121618202425,48912161820242527,4891216182024252728, %U A159903 489121618202425272832,48912161820242527283236 %N A159903 Concatenation of the first n nonsquarefree numbers A013929. %e A159903 a(4) = 48912 is the concatenation 4//8//9//12 of A013929(1) to A013929(4). %Y A159903 Cf. A013929. %K A159903 nonn,base,less %O A159903 1,1 %A A159903 _Jaroslav Krizek_, Apr 25 2009 %E A159903 Slightly edited by _R. J. Mathar_, Apr 28 2009