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 A052672 E.g.f. (1-x)/(1-x-2x^2+x^3). 0
 1, 0, 4, 6, 120, 600, 10080, 95760, 1693440, 23950080, 475372800, 8821612800, 199743667200, 4533271142400, 116906088499200, 3112264995840000, 90679371374592000, 2757644630028288000, 89895729202126848000 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,3 LINKS INRIA Algorithms Project, Encyclopedia of Combinatorial Structures 620 FORMULA E.g.f.: -(-1+x)/(x^3-2*x^2-x+1) Recurrence: {a(1)=0, a(0)=1, a(2)=4, (n^3+6*n^2+11*n+6)*a(n)+(-2*n^2-10*n-12)*a(n+1)+(-n-3)*a(n+2)+a(n+3)=0} Sum(-1/7*_alpha*(-3+_alpha)*_alpha^(-1-n), _alpha=RootOf(_Z^3-2*_Z^2-_Z+1))*n!. a(n) = n!*A052547(n). - R. J. Mathar, Nov 27 2011 MAPLE spec := [S, {S=Sequence(Prod(Z, Union(Z, Prod(Z, Sequence(Z)))))}, labeled]: seq(combstruct[count](spec, size=n), n=0..20); CROSSREFS Sequence in context: A219507 A012934 A013165 * A137025 A176493 A070155 Adjacent sequences:  A052669 A052670 A052671 * A052673 A052674 A052675 KEYWORD easy,nonn AUTHOR encyclopedia(AT)pommard.inria.fr, Jan 25 2000 STATUS approved

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Last modified August 9 22:52 EDT 2020. Contains 336335 sequences. (Running on oeis4.)