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 A061855 #6 May 01 2014 02:47:10 %S A061855 0,2,10,12,42,52,56,170,178,204,212,232,240,682,722,738,812,852,868, %T A061855 920,936,976,992,2730,2762,2866,2898,2978,3010,3244,3276,3380,3412, %U A061855 3492,3524,3640,3672,3752,3784,3888,3920,4000,4032,10922,11082,11146 %N A061855 Symmetric totally balanced binary sequences: those terms of A014486 which are equal to their reversed complement. %C A061855 These encode symmetric (palindromic) structures in many of the Catalan families, e.g. mountain ranges, parenthesizations, unlabeled rooted plane trees. %H A061855 A. Karttunen, <a href="http://www.iki.fi/~kartturi/matikka/tab9766.htm">Some notes on Catalan's Triangle</a> %H A061855 <a href="/index/Par#parens">Index entries for sequences related to parenthesizing</a> %F A061855 a(0) = 0 and the rest with the Maple function map(op, [seq(PalTotBalBinSequences(j), j=1..10)]); %e A061855 E.g. the 45th term 11146 is 10101110001010 in binary and can be interpreted as a parenthesization: ( )( )((( )))( )( ) %p A061855 map(op,[seq(PalTotBalBinSequences(j),j=1..10)]); %p A061855 PalTotBalBinSequences := n -> map(ReflectBinSeq,NonDivingLatticeSequences(n), n); %Y A061855 Obtained by "reflecting" the terms of A061854. Cf. also A035928 (ReflectBinSeq), A061856, A069766. %K A061855 nonn %O A061855 0,2 %A A061855 _Antti Karttunen_, May 11 2001