A085386 E.g.f. cosh(x+x^2/2).

1, 0, 1, 3, 4, 10, 46, 126, 316, 1296, 5356, 17380, 63856, 296088, 1264264, 4940040, 22302736, 110455936, 507711376, 2313783216, 11798364736, 61878663840, 309240315616, 1587272962528, 8792390355904, 48793502304000

Offset: 0

Author

Paul Barry, Jun 27 2003

Keywords

• easy
• nonn

Comments

a(n) is the number of involutions with an even number of cycles. - Geoffrey Critzer, Mar 17 2013

Crossrefs

Cf. A085387.

Programs

Mathematica

nn=25;Range[0,nn]!CoefficientList[Series[Cosh[x+x^2/2],{x,0,nn}],x]  (* Geoffrey Critzer, Mar 17 2013 *)

Formula

a(n)=(A000085(n)+A001464(n))/2