%I #13 Feb 24 2019 11:08:06

%S 1,1,6,52,588,8174,134537,2554647,54909468,1316675221,34820961457,

%T 1006230148609,31529224324159,1064355502971193,38497326001639439,

%U 1484865225798412485,60822449267067095601,2636248249383130776940,120520100503562054999860,5794815395039941996204424

%N Number of hierarchies of hierarchies of hierarchies on n points.

%H N. J. A. Sloane and Thomas Wieder, <a href="https://arxiv.org/abs/math/0307064">The Number of Hierarchical Orderings</a>, arXiv:math/0307064 [math.CO], 2003; Order 21 (2004), 83-89.

%F E.g.f.: exp(f(x)-1) where f(x) = e.g.f. for A075744.

%t m = 20;

%t f[x_] = E^(-1 + E^(-1 + 1/(2 - E^x)));

%t CoefficientList[Exp[f[x] - 1] + O[x]^m, x]*Range[0, m - 1]! (* _Jean-François Alcover_, Feb 24 2019 *)

%Y Cf. A075729, A075744.

%K nonn

%O 0,3

%A _N. J. A. Sloane_, Oct 15 2002