OFFSET
0,3
LINKS
INRIA Algorithms Project, Encyclopedia of Combinatorial Structures 513
FORMULA
Recurrence: {a(1)=1, a(0)=0, (-4-4*n)*a(n)+a(n+1)=0.}
4^(n-1)*n!=n!*A000302(n-1). for n >= 1.
MAPLE
spec := [S, {S=Prod(Z, Sequence(Union(Z, Z, Z, Z)))}, labeled]: seq(combstruct[count](spec, size=n), n=0..20);
MATHEMATICA
With[{nn=20}, CoefficientList[Series[x/(1-4x), {x, 0, nn}], x] Range[0, nn]!] (* Harvey P. Dale, Jan 15 2017 *)
CROSSREFS
KEYWORD
easy,nonn
AUTHOR
encyclopedia(AT)pommard.inria.fr, Jan 25 2000
STATUS
approved