%I A000673 M0355 N0133
%S A000673 0,0,1,0,1,1,2,2,6,8,18,30,67,127,275,551,1192,2507,5475,11820,
%T A000673 26007,57077,126686,281625,630660,1416116,3195784,7232624,16430563,
%U A000673 37429146,85528079,195940960,450074270,1036226173,2391193488,5529420585
%N A000673 Number of bicentered 3-valent (or boron, or binary) trees with n nodes.
%D A000673 N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, 
               Academic Press, 1995 (includes this sequence).
%D A000673 N. J. A. Sloane, A Handbook of Integer Sequences, Academic Press, 1973 
               (includes this sequence).
%D A000673 A. Cayley, On the analytical forms called trees, with application to 
               the theory of chemical combinations, Reports British Assoc. Advance. 
               Sci. 45 (1875), 257-305 = Math. Papers, Vol. 9, 427-460 (see p. 451).
%D A000673 R. C. Read, personal communication.
%H A000673 E. M. Rains and N. J. A. Sloane, <a href="http://www.cs.uwaterloo.ca/
               journals/JIS/index.html">On Cayley's Enumeration of Alkanes (or 4-Valent 
               Trees).</a>, J. Integer Sequences, Vol. 2 (1999), Article 99.1.1.
%H A000673 <a href="Sindx_Tra.html#trees">Index entries for sequences related to 
               trees</a>
%Y A000673 A000672 = A000673 + A000675. Cf. A000022, A000200, A000602.
%Y A000673 Sequence in context: A033760 A136513 A054153 this_sequence A129383 A052957 
               A157253
%Y A000673 Adjacent sequences: A000670 A000671 A000672 this_sequence A000674 A000675 
               A000676
%K A000673 nonn,easy,nice
%O A000673 0,7
%A A000673 N. J. A. Sloane (njas(AT)research.att.com).