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 A097631 Number of unrooted directed trees on n nodes with a green root. 1
 0, 1, 5, 58, 907, 19046, 496869, 15578130, 570573623, 23929861102, 1131235173433, 59529368839898, 3451899685313523, 218712237867226182, 15034642075916533997, 1114519318895861250082, 88631119148029975177327, 7526795487859400166772958, 679859967684397018073935617 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,3 LINKS Table of n, a(n) for n=1..19. C. Banderier, J.-M. Le Bars and V. Ravelomanana, Generating functions for kernels of digraphs, arXiv:math/0411138 [math.CO], 2004. FORMULA a(n) ~ 2^(n-1) * n^(n-2) * (1 - LambertW(1/2)) / (1 + LambertW(1/2)). - Vaclav Kotesovec, Feb 24 2019 MATHEMATICA (* Note: Mathematica's ProductLog is the Lambert W function. *) a[n_] := SeriesCoefficient[-ProductLog[-ProductLog[-2x]/2]/n - ProductLog[-2x] (ProductLog[-2x] + 2)/4, {x, 0, n}] n!; Array[a, 17] (* Jean-François Alcover, Feb 24 2019 *) CROSSREFS Equals A097629(n) - A097630(n). Sequence in context: A129897 A256218 A151424 * A365013 A130768 A195947 Adjacent sequences: A097628 A097629 A097630 * A097632 A097633 A097634 KEYWORD nonn AUTHOR Ralf Stephan, Aug 17 2004 STATUS approved

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Last modified July 13 22:24 EDT 2024. Contains 374288 sequences. (Running on oeis4.)