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 A072771 #3 May 01 2014 02:47:42 %S A072771 0,0,1,0,0,1,2,3,0,0,0,0,0,1,1,2,4,5,3,6,7,8,0,0,0,0,0,0,0,0,0,0,0,0, %T A072771 0,0,1,1,1,1,1,2,2,4,9,10,5,11,12,13,3,3,6,14,15,7,16,17,18,8,19,20, %U A072771 21,22,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0 %N A072771 X-projection of the tabular N X N -> N bijection A072764 and Y-projection of its transpose A072766. %C A072771 This corresponds to Lisp/Scheme function 'car' computed with respect to the lexicographical ordering of parenthesizations/planar binary trees (A014486), i.e. with planar binary trees this is equal to extracting the left subtree (from the root), with general parenthesizations equal to taking the first sub-parenthesization of the top-level list and with general plane trees equal to taking the leftmost branch of the tree (at the root). %H A072771 A. Karttunen, <a href="http://www.iki.fi/~kartturi/matikka/Nekomorphisms/gatomorf.htm">Gatomorphisms</a> (with the complete Scheme source) %K A072771 nonn %O A072771 1,7 %A A072771 _Antti Karttunen_, Jun 12 2002