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