A052840 A simple grammar.

0, 0, 2, 9, 56, 450, 4464, 52920, 731520, 11566800, 206035200, 4083488640, 89137843200, 2124970848000, 54929029478400, 1530259226496000, 45705137084006400, 1456873475016960000, 49362677881380864000

Offset

0,3

Links

Table of n, a(n) for n=0..18.

INRIA Algorithms Project, Encyclopedia of Combinatorial Structures 807

Formula

E.g.f.: log((-1+x)/(-1+2*x))*x.

D-finite with recurrence: {a(1)=0, a(2)=2, (-2*n+2*n^3-4+4*n^2)*a(n)+(-6*n-3*n^2)*a(n+1)+(n+1)*a(n+2)}.

For n > 1, a(n) = n! * (2^(n-1) - 1)/(n-1). - Vaclav Kotesovec, Jun 06 2019

Maple

spec := [S, {B=Sequence(Z, 1 <= card), C=Cycle(B), S=Prod(Z, C)}, labeled]: seq(combstruct[count](spec, size=n), n=0..20);

Mathematica

Flatten[{0, 0, Table[n!*(2^(n-1) - 1)/(n-1), {n, 2, 20}]}] (* Vaclav Kotesovec, Jun 06 2019 *)

Crossrefs

Sequence in context: A158883 A052860 A318289 * A308380 A036243 A364822

Adjacent sequences: A052837 A052838 A052839 * A052841 A052842 A052843

Keyword

easy,nonn

Author

encyclopedia(AT)pommard.inria.fr, Jan 25 2000

Status

approved