A245889 Number of labeled increasing unary-binary trees on n nodes whose breadth-first reading word avoids 312.

1, 1, 3, 8, 29, 110, 469, 2119

Offset

1,3

Comments

The number of labeled increasing unary-binary trees with an associated permutation avoiding 312 in the classical sense. The tree's permutation is found by recording the labels in the order in which they appear in a breadth-first search. (Note that a breadth-first search reading word is equivalent to reading the tree labels left to right by levels, starting with the root.)

In some cases, the same breadth-first 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 labeled increasing trees on four nodes whose permutation avoids 312.

Crossrefs

A245895 gives the number of binary trees instead of unary-binary trees. A245899 gives the number of permutations which avoid 312 that are breadth-first reading words on labeled increasing unary-binary trees.

Sequence in context: A148875 A338306 A148876 * A350907 A013309 A058378

Adjacent sequences: A245886 A245887 A245888 * A245890 A245891 A245892

Keyword

nonn,more

Author

Manda Riehl, Aug 18 2014

Status

approved