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 A046721 #20 Dec 12 2015 15:25:00 %S A046721 1,2,6,16,48,140,428,1308,4072,12796,40432,129432,413900,1342580, %T A046721 4335288,14201804,46226896,152594276,500016036,1660630740,5472190206, %U A046721 18264517264,60475691308,202684618564,673892675030,2266436498400,7562707682032,25510762766704,85394319699916 %N A046721 Number of semi-meanders of order n with 2 components. %H A046721 Andrew Howroyd, <a href="/A046721/b046721.txt">Table of n, a(n) for n = 2..40</a> %H A046721 P. Di Francesco, O. Golinelli and E. Guitter, <a href="http://arXiv.org/abs/hep-th/9506030">Meander, folding and arch statistics</a>, arXiv:hep-th/9506030, 1995. %Y A046721 Cf. A000682, A046726. %K A046721 nonn %O A046721 2,2 %A A046721 _N. J. A. Sloane_ %E A046721 a(15)-a(30) from _Andrew Howroyd_, Nov 27 2015