

A245893


Number of labeled increasing unarybinary trees on n nodes whose breadthfirst reading word simultaneously avoids 231 and 321.


2




OFFSET

1,3


COMMENTS

The number of labeled increasing unarybinary trees with an associated permutation simultaneously avoiding 231 and 321 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 nine trees when n = 4.


EXAMPLE

When n=4, a(n)=9. In the Links above we show the nine labeled increasing trees on four nodes whose permutation simultaneously avoids 231 and 321.


CROSSREFS

A245897 gives the number of binary trees instead of unarybinary trees. A000079 gives the number of permutations which simultaneously avoid 231 and 321 that are breadthfirst reading words on labeled increasing unarybinary trees.
Sequence in context: A145090 A273095 A137953 * A085686 A191412 A246013
Adjacent sequences: A245890 A245891 A245892 * A245894 A245895 A245896


KEYWORD

nonn,more


AUTHOR

Manda Riehl, Aug 22 2014


STATUS

approved



