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



Year-end appeal: Please make a donation to the OEIS Foundation to support ongoing development and maintenance of the OEIS. We are now in our 56th year, we are closing in on 350,000 sequences, and we’ve crossed 9,700 citations (which often say “discovered thanks to the OEIS”).

(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A287221 Number of twice-crossing partitions on n nodes. 2


%S 0,0,0,0,8,42,168,760,2418,10490,30842,131676

%N Number of twice-crossing partitions on n nodes.

%C The meandric numbers A005316 are the numbers of paths which cross themselves 0 times.

%C This sequence is the number of paths that must cross themselves exactly twice.

%H B. W. J. Irwin, <a href="https://www.authorea.com/users/5445/articles/173040-on-the-number-of-k-crossing-partitions/_show_article">On the number of k-crossing partitions</a>

%e a(4) = 8; this is from the partitions

%e (2,1,4,3), (2,4,3,1),

%e (3,2,4,1), (3,4,2,1),

%e (4,1,3,2), (4,2,1,3),

%e (4,2,3,1), (4,3,1,2).

%Y Cf. A005316, A287220.

%K nonn,more

%O 0,5

%A _Benedict W. J. Irwin_, May 22 2017

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 December 3 13:27 EST 2021. Contains 349463 sequences. (Running on oeis4.)