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 A119367 #2 Mar 30 2012 18:59:15
%S A119367 0,0,1,3,6,11,30,126,519,1836,5877,18866,65472,242463,905425,3307371,
%T A119367 11889414,42930441,157641714,586908936,2194106568,8189323686,
%U A119367 30541703733,114219616809,429214875498,1619584557885,6125465491551
%N A119367 Number of rooted planar n-trees whose number of leaves is equal to 2 modulo 3.
%C A119367 a(n)+A119365(n)+A119366(n)=A000108(n).
%F A119367 a(n)=sum{k=0..n, if(mod(n-k,3)=2, (1/n)*C(n,k)*C(n,k+1), 0)}.
%K A119367 easy,nonn
%O A119367 0,4
%A A119367 _Paul Barry_, May 16 2006