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A287220 Number of single-crossing partitions on n nodes. 2


%S 0,0,1,4,10,36,85,312,737,2760,6604,25176

%N Number of single-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 once.

%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(2) = 1, this is from the partition (2,1).

%e a(3) = 4, this is from the partitions (1,3,2),(2,1,3),(2,3,1),(3,1,2).

%Y Cf. A005316, A287221.

%K nonn,more

%O 0,4

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

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Last modified July 13 16:22 EDT 2020. Contains 335688 sequences. (Running on oeis4.)