A245902 Number of permutations of length 2n-1 avoiding 312 that can be realized on increasing binary trees.

1, 2, 7, 37, 222

Offset

1,2

Comments

The number of permutations of length 2n-1 avoiding 312 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 7 permutations of length 5 that avoid 312 and can be realized on increasing binary trees.

Example

For n=3, the a(3)= 7 permutations can be read from the sample trees given in the Links section above.

Crossrefs

A245902 appears to be the terms of A245899 with odd indices. A245895 is the number of increasing unary-binary trees whose breadth-first reading word avoids 312.

Sequence in context: A216362 A002787 A062394 * A063766 A020040 A125191

Adjacent sequences: A245899 A245900 A245901 * A245903 A245904 A245905

Keyword

nonn,more

Author

Manda Riehl, Aug 22 2014

Status

approved