A018225 - OEIS

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

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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