login
A052735
E.g.f. (1-x -sqrt(1-2*x-3*x^2) )/2.
0
0, 0, 2, 6, 48, 480, 6480, 105840, 2056320, 46085760, 1172102400, 33330528000, 1048055500800, 36104266598400, 1352222474803200, 54706557185280000, 2377540306132992000, 110466555918630912000, 5464214679506558976000
OFFSET
0,3
FORMULA
D-finite with recurrence: a(1)=0; a(2)=2; (-3*n^2+3)*a(n)+(-1-2*n)*a(n+1)+a(n+2) = 0.
MAPLE
spec := [S, {C=Prod(B, S), B=Union(S, Z, C), S=Prod(B, Z)}, labeled]: seq(combstruct[count](spec, size=n), n=0..20);
CROSSREFS
Sequence in context: A365285 A052743 A052587 * A365286 A052717 A375022
KEYWORD
easy,nonn
AUTHOR
encyclopedia(AT)pommard.inria.fr, Jan 25 2000
STATUS
approved