%I A000238 M2756 N1108
%S A000238 1,1,3,8,27,91,350,1376,5743,24635,108968,492180,2266502,10598452,
%T A000238 50235931,240872654,1166732814,5702001435,28088787314,139354922608,
%U A000238 695808554300,3494390057212,17641695461662,89495023510876,456009893224285,
               2332997330210440
%N A000238 Number of oriented trees with n nodes.
%D A000238 N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, 
               Academic Press, 1995 (includes this sequence).
%D A000238 N. J. A. Sloane, A Handbook of Integer Sequences, Academic Press, 1973 
               (includes this sequence).
%D A000238 F. Bergeron, G. Labelle and P. Leroux, Combinatorial Species and Tree-Like 
               Structures, Camb. 1998, p. 286.
%D A000238 F. Harary and E. M. Palmer, Graphical Enumeration, Academic Press, NY, 
               1973, p. 60, r(x).
%D A000238 J. Riordan, An Introduction to Combinatorial Analysis, Wiley, 1958, p. 
               138.
%D A000238 R. Simion, Trees with 1-factors and oriented trees, Discrete Math., 88 
               (1991), 93-104.
%H A000238 N. J. A. Sloane, <a href="b000238.txt">Table of n, a(n) for n = 1..350</
               a>
%H A000238 <a href="Sindx_Tra.html#trees">Index entries for sequences related to 
               trees</a>
%F A000238 G.f. = x+x^2+3*x^3+8*x^4+27*x^5+... = R(x)-R(x)^2, where R(x) = g.f. 
               for A000151.
%p A000238 A:= proc(n) option remember; if n=0 then 0 else unapply (convert (series 
               (x*exp (2* add (A(n-1)(x^k)/k, k=1..n-1)), x=0,n), polynom), x) fi 
               end: a:= n-> coeff (series (A(n+1)(x) *(1-A(n+1)(x)), x=0, n+1), 
               x,n): seq (a(n), n=1..26); [From Alois P. Heinz (heinz(AT)hs-heilbronn.de), 
               Aug 20 2008]
%Y A000238 Sequence in context: A148839 A148840 A047153 this_sequence A148841 A148842 
               A148843
%Y A000238 Adjacent sequences: A000235 A000236 A000237 this_sequence A000239 A000240 
               A000241
%K A000238 nonn,easy,nice
%O A000238 1,3
%A A000238 N. J. A. Sloane (njas(AT)research.att.com).
%E A000238 2 errors corrected by Paul Zimmermann Mar 01, 1996.
%E A000238 More terms from N. J. A. Sloane (njas(AT)research.att.com), Mar 10 2007