The OEIS Foundation is supported by donations from users of the OEIS and by a grant from the Simons Foundation.



(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A245896 Number of labeled increasing binary trees on 2n-1 nodes whose breadth-first reading word avoids 321. 3
1, 2, 14, 165, 2639 (list; graph; refs; listen; history; text; internal format)



The number of labeled increasing binary trees with an associated permutation avoiding 321 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.


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

Manda Riehl, For n = 3: the 14 labeled trees on 5 nodes whose associated permutation avoids 321.


When n=3, a(n)=14.  In the Links above we show the fourteen labeled increasing binary trees on five nodes whose permutation avoids 321.


A245890 gives the number of unary-binary trees instead of binary trees.  A245903 gives the number of permutations which avoid 321 that are breadth-first reading words on labeled increasing binary trees.

Sequence in context: A245894 A277362 A209937 * A338632 A124215 A003582

Adjacent sequences:  A245893 A245894 A245895 * A245897 A245898 A245899




Manda Riehl, Aug 22 2014



Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recent
The OEIS Community | Maintained by The OEIS Foundation Inc.

License Agreements, Terms of Use, Privacy Policy. .

Last modified October 20 10:43 EDT 2021. Contains 348100 sequences. (Running on oeis4.)