A104255 a(n) = floor( (2n-1)!!/(2n) ).

0, 0, 2, 13, 94, 866, 9652, 126689, 1914412, 32736453, 624968662, 13176422634, 304071291562, 7623501667031, 206342778454312, 5996836998828457, 186254702081260312, 6156752652130549218, 215810382437839251562, 7995774669321944270390, 312215963278285442939062

Offset

1,3

Comments

Asymptotic estimate for A007769(n).

Links

Table of n, a(n) for n=1..21.

A. Khruzin, Enumeration of chord diagrams

Mathematica

Table[Floor[(2n-1)!!/(2n)], {n, 20}] (* Harvey P. Dale, Nov 12 2012 *)

Crossrefs

Sequence in context: A140636 A369413 A282724 * A369202 A118352 A320360

Adjacent sequences: A104252 A104253 A104254 * A104256 A104257 A104258

Keyword

nonn

Author

Ralf Stephan, Mar 02 2005

Status

approved