%I #18 Jan 05 2021 03:41:46
%S 0,1,2,12,48,360,2160,25200,201600,2540160,25401600,399168000,
%T 4790016000,80951270400,1133317785600,23538138624000,376610217984000,
%U 8180810846208000,147254595231744000,3649353012264960000
%N Unary-binary rooted trees with n nodes.
%C A unary-binary tree is simply a tree in which every node has degree <= 3.
%C Conjecture: for n > 0, a(n) = n! * A040039(n-1). - _Vaclav Kotesovec_, Sep 30 2013
%D F. Bergeron, G. Labelle and P. Leroux, Combinatorial Species and Tree-Like Structures, Camb. 1998, p. 254.
%H <a href="/index/Ro#rooted">Index entries for sequences related to rooted trees</a>
%F E.g.f.: (1-x-sqrt(1-2x-3x^2))/(2x). [Incorrect, this is the o.g.f. for A001006, _Joerg Arndt_, Oct 02 2013]
%K nonn,easy
%O 0,3
%A _N. J. A. Sloane_