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

Author

Ralf Stephan, Mar 02 2005

Keywords

• nonn

Comments

Asymptotic estimate for A007769(n).

Links

• A. Khruzin, Enumeration of chord diagrams

Programs

Mathematica

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