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 A107042 #5 Dec 04 2017 21:35:30 %S A107042 1,1,1,1,2,1,1,2,6,2,12,4 %N A107042 First differences of indices of squarefree Catalan numbers. %C A107042 First differences of A080664. Next term is > 9965. %t A107042 Differences[Position[CatalanNumber[Range[2,50]],_?SquareFreeQ]//Flatten] (* _Harvey P. Dale_, Dec 04 2017 *) %Y A107042 Cf. A000108. %K A107042 nonn %O A107042 0,5 %A A107042 _Paul Barry_, May 09 2005