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 A052645 E.g.f. 2*x^2*(1+x-x^2)/(1-x). 0
 0, 0, 4, 24, 48, 240, 1440, 10080, 80640, 725760, 7257600, 79833600, 958003200, 12454041600, 174356582400, 2615348736000, 41845579776000, 711374856192000, 12804747411456000, 243290200817664000 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,3 LINKS INRIA Algorithms Project, Encyclopedia of Combinatorial Structures 591 FORMULA E.g.f.: 2*x^2*(-x+x^2-1)/(-1+x) Recurrence: {a(1)=0, a(0)=0, (-1-n)*a(n)+a(n+1)=0, a(2)=4, a(3)=24, a(4)=48} 2*n!, n>3. MAPLE spec := [S, {S=Prod(Z, Union(Z, Z), Union(Z, Sequence(Z)))}, labeled]: seq(combstruct[count](spec, size=n), n=0..20); MATHEMATICA With[{nn=20}, CoefficientList[Series[2x^2 (1+x-x^2)/(1-x), {x, 0, nn}], x] Range[0, nn]!] (* Harvey P. Dale, May 14 2017 *) CROSSREFS Sequence in context: A039935 A090821 A226575 * A353250 A191778 A157625 Adjacent sequences:  A052642 A052643 A052644 * A052646 A052647 A052648 KEYWORD easy,nonn AUTHOR encyclopedia(AT)pommard.inria.fr, Jan 25 2000 STATUS approved

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Last modified August 18 02:34 EDT 2022. Contains 356204 sequences. (Running on oeis4.)