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 A045738 Number of branches in all noncrossing rooted trees on n nodes on a circle. 2
 1, 4, 24, 148, 925, 5838, 37128, 237576, 1527867, 9867000, 63946740, 415683216, 2709186844, 17697136408, 115833872400, 759517409424, 4987999112007, 32804320226580, 216018805979760, 1424151150922500, 9398957079664845, 62090203617715350, 410536632908307360 (list; graph; refs; listen; history; text; internal format)
 OFFSET 2,2 LINKS Andrew Howroyd, Table of n, a(n) for n = 2..200 FORMULA a(n) = binomial(3n-3, n-2) - 2*binomial(3n-6, n-3). G.f.: (2*g^3-4*g^2+2*g-1)/((1-3*g)*(g-1)^3) where g*(1-g)^2 = x. - Mark van Hoeij, Nov 10 2011 PROG (PARI) a(n) = binomial(3*n-3, n-2) - 2*binomial(3*n-6, n-3); \\ Andrew Howroyd, Nov 12 2017 (PARI) \\ here b(n) is x^2 * g.f. of A006013. b(n)={serreverse(x-2*x^2+x^3 + O(x^n))} s(n)={(g->(2*g^3-4*g^2+2*g-1)/((1-3*g)*(g-1)^3))(b(n)) + O(x^n)} Vec(s(25)) \\ Andrew Howroyd, Nov 12 2017 CROSSREFS Sequence in context: A072949 A104531 A225050 * A215708 A192806 A262407 Adjacent sequences:  A045735 A045736 A045737 * A045739 A045740 A045741 KEYWORD nonn AUTHOR STATUS approved

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Last modified June 6 04:15 EDT 2020. Contains 334859 sequences. (Running on oeis4.)