A245901 Number of permutations of length 2n-1 avoiding 231 that can be realized on increasing binary trees.

1, 2, 10, 74, 667

Offset

1,2

Comments

The number of permutations of length 2n-1 avoiding 231 in the classical sense which can be realized as labels on an increasing binary tree read in the order they appear in a breadth-first search. (Note that breadth-first 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 breadth-first search reading word, but here we count the permutations, not the trees.

Links

Table of n, a(n) for n=1..5.

Manda Riehl, When n=3, the 10 permutations of length 5 that avoid 231 and can be realizeed on increasing binary trees.

Example

For n=3, the a(3)= 10 permutations can be read from the sample trees given in the Links section above.

Crossrefs

A245901 appears to be the terms of A245898 with odd indices. A245894 is the number of increasing unary-binary trees whose breadth-first reading word avoids 231.

Sequence in context: A151387 A349310 A192259 * A352914 A141149 A306045

Adjacent sequences: A245898 A245899 A245900 * A245902 A245903 A245904

Keyword

nonn,more

Author

Manda Riehl, Aug 22 2014

Status

approved