

A245898


Number of permutations avoiding 231 that can be realized on increasing unarybinary trees with n nodes.


10




OFFSET

1,3


COMMENTS

The number of permutations avoiding 231 in the classical sense which can be realized as labels on an increasing unarybinary tree with n nodes read in the order they appear in a breadthfirst search. (Note that breadthfirst search reading word is equivalent to reading the tree left to right by levels, starting with the root.)
In some cases, more than one tree results in the same breadthfirst search reading word, but here we count the number of permutations, not the number of trees.


LINKS

Table of n, a(n) for n=1..8.


EXAMPLE

For example, when n=4, the permutations 1234, 1243, 1324, and 1423 all avoid 231 in the classical sense and occur as breadthfirst search reading words on an increasing unarybinary tree with 4 nodes:
1 1 1 1
/ \ / \ / \ / \
2 3 2 4 3 2 4 2
   
4 3 4 3


CROSSREFS

A245901 is the terms of A245898 with odd indices. A245888 is the number of increasing unarybinary trees whose breadthfirst reading word avoids 231.
Sequence in context: A049130 A101488 A279544 * A230662 A206464 A089429
Adjacent sequences: A245895 A245896 A245897 * A245899 A245900 A245901


KEYWORD

nonn,more


AUTHOR

Manda Riehl, Aug 05 2014


STATUS

approved



