%I A003092 M2159
%S A003092 0,1,2,36,1200,57000,3477600,257826240,22438563840,2238543216000,
%T A003092 251584613280000,31431367287936000,4319334744012288000,647313578549730892800,
%U A003092 105041172967733882880000,18345770194541665075200000,3430869798262479024291840000
%N A003092 Number of labeled plane 2-trees with n nodes.
%D A003092 N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, 
               Academic Press, 1995 (includes this sequence).
%D A003092 E. M. Palmer and R. C. Read, on the number of plane 2-trees, J. Lond. 
               Math. Soc., 6 (1973), 583-592.
%D A003092 F. Harary and E. Palmer, Graphical Enumeration, (1973), p. 30, Problem 
               1.14.
%H A003092 <a href="Sindx_Tra.html#trees">Index entries for sequences related to 
               trees</a>
%F A003092 n(n-1)^2 (5n-10)!/(4n-6)!.
%p A003092 [ seq(n*(n-1)^2*(5*n-10)!/(4*n-6)!,n=2..20) ];
%Y A003092 Sequence in context: A166473 A009539 A009554 this_sequence A046673 A088026 
               A126934
%Y A003092 Adjacent sequences: A003089 A003090 A003091 this_sequence A003093 A003094 
               A003095
%K A003092 nonn
%O A003092 1,3
%A A003092 N. J. A. Sloane (njas(AT)research.att.com).