A018225 Number of connected chord diagrams of degree n.

1, 1, 2, 6, 31, 255, 2788, 37333, 578799, 10134071, 197394232, 4231417728, 98991987830, 2510081238264, 68583045013542, 2009094843480565, 62824038815664719, 2088829704241946181, 73591470349452760456, 2738742863175749456078

Offset

1,3

Links

Table of n, a(n) for n=1..20.

Alexander Stoimenow, On the number of chord diagrams, Discr. Math. 218 (2000), 209-233.

Formula

a(n) = A007769(n) - A317184(n). - Sean A. Irvine, Feb 05 2019

Mathematica

Stoimenow states that a Mma package is available from his website. - N. J. A. Sloane, Jul 26 2018

Crossrefs

Sequence in context: A094639 A113719 A369767 * A217143 A075845 A003087

Adjacent sequences: A018222 A018223 A018224 * A018226 A018227 A018228

Keyword

nonn

Author

Alexander Stoimenow (stoimeno(AT)mail.informatik.hu-berlin.de)

Extensions

More terms from Sean A. Irvine, Feb 05 2019

Status

approved