A085386 - OEIS

%I #7 Mar 17 2013 10:48:54

%S 1,0,1,3,4,10,46,126,316,1296,5356,17380,63856,296088,1264264,4940040,

%T 22302736,110455936,507711376,2313783216,11798364736,61878663840,

%U 309240315616,1587272962528,8792390355904,48793502304000

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

%C a(n) is the number of involutions with an even number of cycles. - _Geoffrey Critzer_, Mar 17 2013

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

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

%Y Cf. A085387.

%K easy,nonn

%O 0,4

%A _Paul Barry_, Jun 27 2003