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

 

Logo


Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A245902 Number of permutations of length 2n-1 avoiding 312 that can be realized on increasing binary trees. 3

%I

%S 1,2,7,37,222

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

%C 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.)

%C 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.

%H Manda Riehl, <a href="/A245902/a245902.png">When n=3, the 7 permutations of length 5 that avoid 312 and can be realized on increasing binary trees.</a>

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

%Y 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.

%K nonn,more

%O 1,2

%A _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 February 17 02:22 EST 2020. Contains 331976 sequences. (Running on oeis4.)