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A287220 Number of single-crossing partitions on n nodes. 2
0, 0, 1, 4, 10, 36, 85, 312, 737, 2760, 6604, 25176 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,4

COMMENTS

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

This sequence is the number of paths that must cross themselves exactly once.

LINKS

Table of n, a(n) for n=0..11.

B. W. J. Irwin, On the number of k-crossing partitions

EXAMPLE

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

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

CROSSREFS

Cf. A005316, A287221.

Sequence in context: A222506 A108596 A204270 * A220205 A196880 A088013

Adjacent sequences:  A287217 A287218 A287219 * A287221 A287222 A287223

KEYWORD

nonn,more

AUTHOR

Benedict W. J. Irwin, May 22 2017

STATUS

approved

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Last modified May 25 07:53 EDT 2020. Contains 334584 sequences. (Running on oeis4.)