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A052768
A simple grammar.
0
0, 0, 0, 0, 0, 120, 360, 840, 1680, 3024, 5040, 7920, 11880, 17160, 24024, 32760, 43680, 57120, 73440, 93024, 116280, 143640, 175560, 212520, 255024, 303600, 358800, 421200, 491400, 570024, 657720, 755160, 863040, 982080, 1113024
OFFSET
0,6
FORMULA
a(n)=0, n <= 4; a(n) = n*(n-1)*(n-2)*(n-3), n >= 5.
G.f.: 24*x^5*(5-10*x+10*x^2-5*x^3+x^4)/(1-x)^5. [Colin Barker, Jun 25 2012]
MAPLE
spec := [S, {B=Set(Z, 1 <= card), S=Prod(Z, Z, Z, Z, B)}, labeled]: seq(combstruct[count](spec, size=n), n=0..20);
CROSSREFS
Sequence in context: A118058 A269037 A144524 * A242845 A234915 A061218
KEYWORD
easy,nonn
AUTHOR
encyclopedia(AT)pommard.inria.fr, Jan 25 2000
EXTENSIONS
More terms and corrected formula from Larry Reeves (larryr(AT)acm.org), Jan 23 2001
STATUS
approved