

A097392


The number of hierarchies with at least one subhierarchy composed of exactly 3 levels and no subhierarchy with more than 3 levels.


1




OFFSET

1,4


LINKS

Table of n, a(n) for n=1..10.
N. J. A. Sloane and Thomas Wieder, The Number of Hierarchical Orderings, Order 21 (2004), 8389.


EXAMPLE

Let : denote the separation between two subhierarchies, e.g. 2:3 are two subhierarchies where subhierarchy s=1 contains two elements and subhierarchy s=2 contains three elements. Let  denote the separation between two levels, e.g. 221 is a hierarchy composed of three levels with two elements on levels l=1 and l=2 and one element on level l=3. For n=5 one has a(5) = 12 hierarchies where at least one subhierarchy has exactly 3 levels (and no level l > 3 is allowed):
311; 131; 113; 221; 212; 122; 111:2; 111:1:1; 111:11;
211:1; 121:1; 112:1.


CROSSREFS

Cf. A034691, A097237, A097391, A000041.
Sequence in context: A260145 A260778 A118885 * A090634 A260186 A097067
Adjacent sequences: A097389 A097390 A097391 * A097393 A097394 A097395


KEYWORD

nonn


AUTHOR

Thomas Wieder, Aug 13 2004


STATUS

approved



