

A245889


Number of labelled increasing unarybinary trees on n nodes whose breadthfirst reading word avoids 312.


3




OFFSET

1,3


COMMENTS

The number of labelled increasing unarybinary trees with an associated permutation avoiding 312 in the classical sense. The tree’s permutation is found by recording the labels in the order 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 8 trees when n = 4.


EXAMPLE

When n=4, a(n)=8. In the Links above we show the eight labelled increasing trees on four nodes whose permutation avoids 312.


CROSSREFS

A245895 gives the number of binary trees instead of unarybinary trees. A245899 gives the number of permutations which avoid 312 that are breadthfirst reading words on labelled increasing unarybinary trees.
Sequence in context: A022017 A148875 A148876 * A013309 A058378 A063839
Adjacent sequences: A245886 A245887 A245888 * A245890 A245891 A245892


KEYWORD

nonn


AUTHOR

Manda Riehl, Aug 18 2014


STATUS

approved



