

A245888


Number of labeled increasing unarybinary trees on n nodes whose breadthfirst reading word avoids 231.


7




OFFSET

1,3


COMMENTS

The number of labeled increasing unarybinary trees with an associated permutation avoiding 231 in the classical sense. The tree's permutation is found by recording the labels in the order in which they appear in a breadthfirst search. (Note that a breadthfirst search reading word is equivalent to reading the tree labels left to right by levels, starting with the root.)
In some cases, the same breadthfirst search reading permutation can be found on differently shaped trees. This sequence gives the number of trees, not the number of permutations.


LINKS

Table of n, a(n) for n=1..8.
Manda Riehl, The 9 trees when n = 4.


EXAMPLE

The a(4) = 9 such trees are:
:
: 1 1 1 1
: /\ /\ /\ /\
: 2 3 2 3 3 2 3 2
:    
: 4 4 4 4
:
:
: 1 1 1 1 1
: /\ /\   
: 2 4 4 2 2 2 2
:   /\ /\ 
: 3 3 3 4 4 3 3
: 
: 4
:


CROSSREFS

A245894 gives the number of such binary trees instead of unarybinary trees.
A245898 gives the number of permutations which avoid 231 that are breadthfirst reading words on labeled increasing unarybinary trees instead of the number of trees.
Sequence in context: A106435 A276368 A058540 * A295739 A156016 A032314
Adjacent sequences: A245885 A245886 A245887 * A245889 A245890 A245891


KEYWORD

nonn,more


AUTHOR

Manda Riehl, Aug 18 2014


STATUS

approved



