%I A000060 M0904 N0340
%S A000060 1,2,3,10,27,98,350,1402,5743,24742,108968,492638,2266502,10600510,
%T A000060 50235931,240882152,1166732814,5702046382,28088787314,139355139206,
%U A000060 695808554300,3494391117164,17641695461662,89495028762682,456009893224285,
               2332997356507678,11980753878699716,61739654456234062,319188605907760846
%N A000060 Number of signed trees with n nodes.
%D A000060 F. Harary and G. Prins, The number of homeomorphically irreducible trees 
               and other species, Acta Math., 101 (1959), 141-162.
%D A000060 P. Leroux and B. Miloudi, ``G\'{e}n\'{e}ralisations de la formule d'Otter,
               '' Ann. Sci. Math. Qu\'{e}bec, Vol. 16, No. 1, pp. 53-80, 1992.
%D A000060 N. J. A. Sloane, A Handbook of Integer Sequences, Academic Press, 1973 
               (includes this sequence).
%D A000060 N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, 
               Academic Press, 1995 (includes this sequence).
%H A000060 T. D. Noe, <a href="b000060.txt">Table of n, a(n) for n=1..500</a>
%H A000060 F. Harary and G. Prins, <a href="http://www.actamathematica.org/Secure/
               archive/finalv101/am101p01a00141.pdf">The number of homeomorphically 
               irreducible trees and other species</a>, Acta Math., 101 (1959), 
               141-162.
%H A000060 P. Leroux and B. Miloudi, <a href="http://www.labmath.uqam.ca/~annales/
               english/volumes/16-1/53.html">Generalisations de la formule d'Otter</
               a>, Ann. Sci. Math. Quebec 16 (1992), no 1, 53-80.
%H A000060 <a href="Sindx_Tra.html#trees">Index entries for sequences related to 
               trees</a>
%F A000060 Generating function A(x) is such that A(x)=S(x)+S(x^2)-S(x)^2, where 
               S(x) is the generating function for A000151 - Pab Ter (pabrlos2(AT)yahoo.com), 
               Oct 12 2005
%p A000060 unassign('x'): with(combstruct): norootree:=[S, {B = Set(S), S = Prod(Z,
               B,B)}, unlabeled]: S:=x->add(count(norootree,size=i)*x^i,i=1..30): 
               seq(coeff(S(x)+S(x^2)-S(x)^2,x,i),i=1..29);# with Algolib (Pab Ter)
%Y A000060 Sequence in context: A052929 A151415 A134588 this_sequence A089752 A007029 
               A099435
%Y A000060 Adjacent sequences: A000057 A000058 A000059 this_sequence A000061 A000062 
               A000063
%K A000060 nonn,nice
%O A000060 1,2
%A A000060 N. J. A. Sloane (njas(AT)research.att.com).
%E A000060 More terms from Pab Ter (pabrlos2(AT)yahoo.com), Oct 12 2005