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 A075756 Number of hierarchies of hierarchies of hierarchies on n points. 1
 1, 1, 6, 52, 588, 8174, 134537, 2554647, 54909468, 1316675221, 34820961457, 1006230148609, 31529224324159, 1064355502971193, 38497326001639439, 1484865225798412485, 60822449267067095601, 2636248249383130776940, 120520100503562054999860, 5794815395039941996204424 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,3 LINKS Table of n, a(n) for n=0..19. N. J. A. Sloane and Thomas Wieder, The Number of Hierarchical Orderings, arXiv:math/0307064 [math.CO], 2003; Order 21 (2004), 83-89. FORMULA E.g.f.: exp(f(x)-1) where f(x) = e.g.f. for A075744. MATHEMATICA m = 20; f[x_] = E^(-1 + E^(-1 + 1/(2 - E^x))); CoefficientList[Exp[f[x] - 1] + O[x]^m, x]*Range[0, m - 1]! (* Jean-François Alcover, Feb 24 2019 *) CROSSREFS Cf. A075729, A075744. Sequence in context: A355162 A127133 A243249 * A363008 A217486 A144345 Adjacent sequences: A075753 A075754 A075755 * A075757 A075758 A075759 KEYWORD nonn AUTHOR N. J. A. Sloane, Oct 15 2002 STATUS approved

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Last modified May 26 05:37 EDT 2024. Contains 372807 sequences. (Running on oeis4.)