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E.g.f. x^4*(1+x-x^2)/(1-x).
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%I #11 Apr 18 2017 07:03:59

%S 0,0,0,0,24,240,720,5040,40320,362880,3628800,39916800,479001600,

%T 6227020800,87178291200,1307674368000,20922789888000,355687428096000,

%U 6402373705728000,121645100408832000,2432902008176640000

%N E.g.f. x^4*(1+x-x^2)/(1-x).

%H INRIA Algorithms Project, <a href="http://ecs.inria.fr/services/structure?nbr=610">Encyclopedia of Combinatorial Structures 610</a>

%F E.g.f.: x^4*(-x+x^2-1)/(-1+x)

%F Recurrence: {a(1)=0, a(0)=0, a(2)=0, (-1-n)*a(n)+a(n+1)=0, a(3)=0, a(4)=24, a(6)=720, a(5)=240}

%F n! for n >= 4.

%p spec := [S,{S=Prod(Z,Z,Z,Z,Union(Z,Sequence(Z)))},labeled]: seq(combstruct[count](spec,size=n), n=0..20);

%K easy,nonn

%O 0,5

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