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 A101613 #2 Apr 30 2014 01:26:48 %S A101613 3,26,684,35664,3068640,392722560,69878833920,16484477184000, %T A101613 4976250951168000,1870345490614272000,856314330237628416000, %U A101613 469109144339151224832000,302956190548293037916160000 %N A101613 (2n)! * Sum[k=n..2n, 1/k]. %Y A101613 Cf. A101609, A101610, A101611, A101612, A000254, A046673, A052517. %K A101613 nonn,easy %O A101613 1,1 %A A101613 _Ralf Stephan_, Dec 10 2004