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 A052745 A simple grammar. 1

%I

%S 0,0,0,6,24,110,600,3836,28224,235224,2191680,22584672,255087360,

%T 3134139840,41620400640,594082771200,9070900715520,147531542054400,

%U 2546434166169600,46489412442009600,895079522340864000,18125736166340812800,385129713617510400000

%N A simple grammar.

%H INRIA Algorithms Project, <a href="http://ecs.inria.fr/services/structure?nbr=701">Encyclopedia of Combinatorial Structures 701</a>

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

%F Recurrence: a(1)=0, a(2)=0, a(3)=6, (-n+n^4+n^3-3*n^2+2)*a(n)+(-2*n^3-3*n^2+2*n)*a(n+1)+(n^2+n)*a(n+2)=0.

%F a(n) = (-1)^(n+1)*2*n*Stirling1(n-1, 2). - _Vladeta Jovovic_, Nov 08 2003

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

%t Range[0, 30]! CoefficientList[Series[Log[-1/(-1 + x)]^2 x,{x, 0, 30}], x] (* _Vincenzo Librandi_, Jul 08 2015 *)

%o (Maxima) makelist((-1)^(n+1)*2*n*stirling1(n-1, 2), n, 0, 20); /* _Bruno Berselli_, May 25 2011 */

%o (MAGMA) [0] cat [(-1)^(n+1)*2*n*StirlingFirst(n-1, 2): n in [1..30]]; // _Vincenzo Librandi_, Jul 08 2015

%K easy,nonn

%O 0,4

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

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Last modified September 20 05:17 EDT 2021. Contains 347577 sequences. (Running on oeis4.)