A287220 Number of single-crossing partitions on n nodes.

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

Offset: 0

Author

Benedict W. J. Irwin, May 22 2017

Keywords

• nonn
• more

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.

Examples

			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).
		

Links

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

Crossrefs

Cf. A005316, A287221.