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 A052689 E.g.f. (1+x-x^2)/((1-x)(1-x^2)). 1
 1, 2, 4, 18, 72, 480, 2880, 25200, 201600, 2177280, 21772800, 279417600, 3353011200, 49816166400, 697426329600, 11769069312000, 188305108992000, 3556874280960000, 64023737057280000, 1338096104497152000 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,2 LINKS Vincenzo Librandi, Table of n, a(n) for n = 0..200 INRIA Algorithms Project, Encyclopedia of Combinatorial Structures 637 FORMULA E.g.f.: -(-x+x^2-1)/(-1+x)/(-1+x^2) Recurrence: {a(0)=1, a(2)=4, a(1)=2, (-14*n-n^3-7*n^2-8)*a(n)+(-2-n)*a(n+1)+(n+3)*a(n+2)=0} (1/4*(-1)^(1-n)+1/2*n+5/4)*n!. a(n) = n!*A004526(n+3). - R. J. Mathar, Nov 27 2011 MAPLE spec := [S, {S=Prod(Union(Z, Sequence(Z)), Sequence(Prod(Z, Z)))}, labeled]: seq(combstruct[count](spec, size=n), n=0..20); MATHEMATICA With[{nn=20}, CoefficientList[Series[(1+x-x^2)/((1-x)(1-x^2)), {x, 0, nn}], x] Range[0, nn]!] (* Harvey P. Dale, Feb 10 2014 *) CROSSREFS Sequence in context: A303352 A226011 A325850 * A139104 A014448 A277033 Adjacent sequences:  A052686 A052687 A052688 * A052690 A052691 A052692 KEYWORD easy,nonn AUTHOR encyclopedia(AT)pommard.inria.fr, Jan 25 2000 STATUS approved

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Last modified March 30 12:10 EDT 2020. Contains 333125 sequences. (Running on oeis4.)