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 A104256 #2 Apr 30 2014 01:31:04 %S A104256 0,0,1,6,47,433,4826,63344,957206,16368226,312484331,6588211317, %T A104256 152035645781,3811750833515,103171389227156,2998418499414228, %U A104256 93127351040630156,3078376326065274609,107905191218919625781 %N A104256 [ (2n-1)!!/(4n) ]. %C A104256 Asymptotic estimate for A054499(n). %H A104256 A. Khruzin, <a href="http://arXiv.org/abs/math.CO/0008209">Enumeration of chord diagrams</a> %K A104256 nonn %O A104256 1,4 %A A104256 _Ralf Stephan_, Mar 02 2005