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 A072773 #3 May 01 2014 02:47:42 %S A072773 1,3,6,7,16,42,8,19,51,52,17,44,126,127,385,18,47,135,136,413,414,20, %T A072773 53,154,155,475,476,477,21,56,163,164,503,504,505,506,22,60,177,178, %U A072773 551,552,553,554,555,45,128,390,391,1243,1244,1245,1246,1247,4089,46 %N A072773 The upper triangular region of A072764. %H A072773 A. Karttunen, <a href="http://www.iki.fi/~kartturi/matikka/Nekomorphisms/gatomorf.htm">Gatomorphisms</a> (with the complete Scheme source) %o A072773 (Scheme function showing the general idea:) (define (A072773 n) (CatalanRankGlobal (parenthesization->binexp (cons (binexp->parenthesization (A014486 (A003056 n))) (binexp->parenthesization (A014486 (A002262 n))))))) %Y A072773 Cf. also A014486, A003056, A002262. %K A072773 nonn,tabl %O A072773 0,2 %A A072773 _Antti Karttunen_, Jun 12 2002