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A245892 Number of labelled increasing unary-binary trees on n nodes whose breadth-first reading word simultaneously avoids 231 and 312 (or avoids 312 and 321). 1
1, 1, 3, 8, 28, 102, 407, 1701 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,3

COMMENTS

The number of labelled increasing unary-binary trees with an associated permutation avoiding 231 and 312 simultaneously (or avoids 312 and 321 simultaneously) in the classical sense.  The tree’s permutation is found by recording the labels in the order 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 eight trees when n=4.

EXAMPLE

When n=4, a(n)=8.  In the Links above we show the eight labelled increasing trees on four nodes whose permutation simultaneously avoids 231 and 312.

CROSSREFS

A111554 gives the number of binary trees instead of unary-binary trees.

A002083 gives the number of permutations which avoid 231 and 312 simultaneously that are breadth-first reading words on labelled increasing unary-binary trees.

Sequence in context: A026627 A148866 A151431 * A263103 A093356 A224271

Adjacent sequences:  A245889 A245890 A245891 * A245893 A245894 A245895

KEYWORD

nonn,more

AUTHOR

Manda Riehl, Aug 19 2014

STATUS

approved

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Last modified February 19 09:13 EST 2018. Contains 299330 sequences. (Running on oeis4.)