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A245888 Number of labeled increasing unary-binary trees on n nodes whose breadth-first reading word avoids 231. 7
1, 1, 3, 9, 36, 155, 752, 3894 (list; graph; refs; listen; history; text; internal format)
OFFSET
1,3
COMMENTS
The number of labeled increasing unary-binary trees with an associated permutation avoiding 231 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
EXAMPLE
The a(4) = 9 such trees are:
:
: 1 1 1 1
: /\ /\ /\ /\
: 2 3 2 3 3 2 3 2
: | | | |
: 4 4 4 4
:
:
: 1 1 1 1 1
: /\ /\ | | |
: 2 4 4 2 2 2 2
: | | /\ /\ |
: 3 3 3 4 4 3 3
: |
: 4
:
CROSSREFS
A245894 gives the number of such binary trees instead of unary-binary trees.
A245898 gives the number of permutations which avoid 231 that are breadth-first reading words on labeled increasing unary-binary trees instead of the number of trees.
Sequence in context: A276368 A058540 A350451 * A295739 A156016 A032314
KEYWORD
nonn,more
AUTHOR
Manda Riehl, Aug 18 2014
STATUS
approved

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Last modified March 18 22:34 EDT 2024. Contains 370951 sequences. (Running on oeis4.)