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

0,4

Comments

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

Links

Table of n, a(n) for n=0..25.

Formula

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

Mathematica

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

Crossrefs

Cf. A085387.

Sequence in context: A218293 A374313 A288110 * A290517 A295824 A180696

Adjacent sequences: A085383 A085384 A085385 * A085387 A085388 A085389

Keyword

easy,nonn

Author

Paul Barry, Jun 27 2003

Status

approved