OFFSET
0,4
LINKS
Anwar Al Ghabra, K. Gopala Krishna, Patrick Labelle, and Vasilisa Shramchenko, Enumeration of multi-rooted plane trees, arXiv:2301.09765 [math.CO], 2023.
Vincent Pilaud and Juanjo Rué, Analytic combinatorics of chord and hyperchord diagrams with k crossings, arXiv preprint arXiv:1307.6440, 2013
Henry Bottomley, Illustration for A000108, A001147, A002694, A067310 and A067311
FORMULA
EXAMPLE
a(3)=3 since the only possibility is to have one of the three chords intersected by the other two.
MATHEMATICA
Table[Binomial[2n, n-2] (n-2)/2, {n, 0, 30}] (* Harvey P. Dale, Nov 04 2011 *)
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Henry Bottomley, Oct 06 2002
STATUS
approved