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 A000151 Number of oriented rooted trees with n nodes. Also rooted trees with n nodes and 2-colored non-root nodes. (Formerly M1770 N0701) 12
 1, 2, 7, 26, 107, 458, 2058, 9498, 44947, 216598, 1059952, 5251806, 26297238, 132856766, 676398395, 3466799104, 17873508798, 92630098886, 482292684506, 2521610175006, 13233573019372, 69687684810980, 368114512431638, 1950037285256658, 10357028326495097, 55140508518522726, 294219119815868952, 1573132563600386854, 8427354035116949486, 45226421721391554194 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 REFERENCES F. Bergeron, G. Labelle and P. Leroux, Combinatorial Species and Tree-Like Structures, Camb. 1998, p. 286. S. R. Finch, Mathematical Constants, Cambridge, 2003, p. 307 and 564. F. Harary and E. M. Palmer, Graphical Enumeration, Academic Press, NY, 1973, p. 60, R(x). J. Riordan, An Introduction to Combinatorial Analysis, Wiley, 1958, p. 138. N. J. A. Sloane, A Handbook of Integer Sequences, Academic Press, 1973 (includes this sequence). N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence). LINKS N. J. A. Sloane, Table of n, a(n) for n = 1..500 L. Foissy, Algebraic structures on typed decorated rooted trees, arXiv:1811.07572 [math.RA], 2018. Vsevolod Gubarev, Rota-Baxter operators on a sum of fields, arXiv:1811.08219 [math.RA], 2018. INRIA Algorithms Project, Encyclopedia of Combinatorial Structures 387 P. Leroux and B. Miloudi, Generalisations de la formule d'Otter, Ann. Sci. Math. Quebec 16 (1992), no 1, 53-80. P. Leroux and B. Miloudi, Généralisations de la formule d'Otter, Ann. Sci. Math. Québec, Vol. 16, No. 1, pp. 53-80, 1992. (Annotated scanned copy) R. J. Mathar, Topologically Distinct Sets of Non-intersecting Circles in the Plane, arXiv:1603.00077 [math.CO], 2016. R. Simon, Trees with 1-factors and oriented trees, Discrete Math., 88 (1981), 97. R. Simon, Trees with 1-factors and oriented trees, Discrete Math., 88 (1981), 97. (Annotated scanned copy) S. G. Wagner, An identity for the cycle indices of rooted tree automorphism groups, Elec. J. Combinat., 13 (2006), #R00. FORMULA Generating function A(x) = x+2*x^2+7*x^3+26*x^4+... satisfies A(x)=x*exp( 2*sum_{k>=1}(A(x^k)/k) ) [Harary]. - Pab Ter (pabrlos2(AT)yahoo.com), Oct 12 2005 G.f.: x*Product_{n>=1} 1/(1 - x^n)^(2*a(n)) = Sum_{n>=1} a(n)*x^n. a(n) ~ c * d^n / n^(3/2), where d = A245870 = 5.64654261623294971289271351621..., c = 0.207861597422917421321653492... . - Vaclav Kotesovec, Aug 20 2014 MAPLE R:=series(x+2*x^2+7*x^3+26*x^4, x, 5); M:=500; for n from 5 to M do series(add( subs(x=x^k, R)/k, k=1..n-1), x, n); t4:=coeff(series(x*exp(%)^2, x, n+1), x, n); R:=series(R+t4*x^n, x, n+1); od: for n from 1 to M do lprint(n, coeff(R, x, n)); od: # N. J. A. Sloane, Mar 10 2007 with(combstruct):norootree:=[S, {B = Set(S), S = Prod(Z, B, B)}, unlabeled] :seq(count(norootree, size=i), i=1..30); # with Algolib (Pab Ter) MATHEMATICA terms = 30; A[_] = 0; Do[A[x_] = x*Exp[2*Sum[A[x^k]/k, {k, 1, terms}]] + O[x]^(terms+1) // Normal, terms+1]; CoefficientList[A[x], x] // Rest (* Jean-François Alcover, Jun 08 2011, updated Jan 11 2018 *) PROG (PARI) seq(N) = {my(A=vector(N, j, 1)); for (n=1, N-1, A[n+1] = 2/n * sum(i=1, n, sumdiv(i, d, d*A[d]) * A[n-i+1] ) ); A} \\ Andrew Howroyd, May 13 2018 CROSSREFS Cf. A000238, A038055. Also the self-convolution of A005750. - Paul D. Hanna, Aug 17 2002 Column k=2 of A242249. Cf. A005751, A245870. Sequence in context: A150565 A150566 A150567 * A150568 A102319 A006603 Adjacent sequences:  A000148 A000149 A000150 * A000152 A000153 A000154 KEYWORD nonn,eigen,nice AUTHOR EXTENSIONS Extended with alternate description by Christian G. Bower, Apr 15 1998 More terms from Pab Ter (pabrlos2(AT)yahoo.com), Oct 12 2005 STATUS approved

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Last modified October 15 20:04 EDT 2019. Contains 328037 sequences. (Running on oeis4.)