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 A186308 #11 May 18 2013 13:28:17 %S A186308 0,0,0,0,1,3,11,33,95,260,696,1816,4659,11795,29520,73267,180485, %T A186308 442157,1077856,2617726,6336551,15299287,36857178,88635225,212829307, %U A186308 510416549,1222826994,2927083468,7001510693,16737477645 %N A186308 Number of lobsters with n nodes that are not caterpillars. %H A186308 Wikipedia, <a href="http://en.wikipedia.org/wiki/Caterpillar_tree">Caterpillar tree</a> %F A186308 a(n) = A130131(n) - (2^(n-4) + 2^[(n-4)/2]). %e A186308 All the trees of order less than 7 are caterpillars. Only one tree with 7 nodes is a lobster and is not a caterpillar, so a(3)=a(4)=a(5)=a(6)=0, and a(7)=1. %Y A186308 Cf. A000055, A130131. %K A186308 nonn %O A186308 3,6 %A A186308 _Washington Bomfim_, Feb 23 2011