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 A080664 #12 Mar 25 2015 00:25:58 %S A080664 1,2,3,4,5,7,8,9,11,17,19,31,35 %N A080664 Numbers n such that n-th Catalan number is squarefree. %C A080664 No more terms < 10000. - _Robert G. Wilson v_, Aug 28 2004 %H A080664 C. Rivera, <a href="http://www.primepuzzles.net/problems/prob_043.htm">Problem 43. Catalan Numbers</a> in www.primepuzzles.net %t A080664 Select[Range[500], SquareFreeQ[CatalanNumber[ # ]] &] %Y A080664 Cf. A000108. %K A080664 nonn %O A080664 1,2 %A A080664 _Joseph L. Pe_, Mar 01 2003 %E A080664 Mathematica updated by _Jean-François Alcover_, Jul 04 2013