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0, 0, 0, 6, 24, 70, 180, 434, 1008, 2286, 5100, 11242, 24552, 53222, 114660, 245730, 524256, 1114078, 2359260, 4980698, 10485720, 22020054, 46137300, 96468946, 201326544, 419430350, 872415180, 1811939274, 3758096328, 7784628166, 16106127300, 33285996482
(list; graph; refs; listen; history; internal format)
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OFFSET
| 0,4
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LINKS
| INRIA Algorithms Project, Encyclopedia of Combinatorial Structures 705
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FORMULA
| E.g.f.: exp(x)^2*x-2*x*exp(x)+x
Recurrence: {a(1)=0, a(2)=0, a(3)=6, (2*n^2+6*n+4)*a(n)+(-6*n-3*n^2)*a(n+1)+(n^2+n)*a(n+2)}
Sum(n*2^(k-2), k=3..n). - Zerinvary Lajos (zerinvarylajos(AT)yahoo.com), Oct 09 2006
a(n) = n*(2^(n-1)-2), n>=3. - Mitch Harris (Harris.Mitchell(AT)mgh.harvard.edu), Oct 25 2006
O.g.f.: 2*x^3*(3-6*x+2*x^2)/((-1+x)^2*(-1+2*x)^2). - R. J. Mathar (mathar(AT)strw.leidenuniv.nl), Dec 05 2007
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MAPLE
| spec := [S, {B=Set(Z, 1 <= card), S=Prod(Z, B, B)}, labeled]: seq(combstruct[count](spec, size=n), n=0..20);
g := taylor(exp(x)^2*x-2*x*exp(x)+x, x=0, 121): q := seq(coeff(g, x, i)*i!, i=0..120);
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MATHEMATICA
| Table[If[n < 3, 0, (n*(2^n - 3) - n)/2], {n, 0, 200}] (* From Vladimir Joseph Stephan Orlovsky, Jun 30 2011 *)
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CROSSREFS
| Sequence in context: A101877 A092348 A006528 * A090574 A080373 A180437
Adjacent sequences: A052746 A052747 A052748 * A052750 A052751 A052752
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KEYWORD
| easy,nonn
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AUTHOR
| encyclopedia(AT)pommard.inria.fr, Jan 25 2000
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EXTENSIONS
| Better description from Victor Adamchik (adamchik(AT)cs.cmu.edu), Jul 19 2001
More terms from Sascha Kurz (sascha.kurz(AT)uni-bayreuth.de), Mar 25 2002
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