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A034866
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a(n) = n!*(n-4)/2, n > 4, and a(4) = 4.
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1
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4, 60, 720, 7560, 80640, 907200, 10886400, 139708800, 1916006400, 28021593600, 435891456000, 7192209024000, 125536739328000, 2311968282624000, 44816615940096000, 912338253066240000
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OFFSET
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4,1
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LINKS
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FORMULA
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(-n+5)*a(n) + n*(n-4)*a(n-1) = 0. - R. J. Mathar, Apr 03 2017
E.g.f.: x^4*(1 + x + x^2)/(6*(1 - x)^2). - G. C. Greubel, Feb 16 2018
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MAPLE
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[4, seq(factorial(n)*(n-4)/2, n=5..20)]; # Muniru A Asiru, Feb 17 2018
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MATHEMATICA
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Join[{4}, Table[n!*(n-4)/2, {n, 5, 30}]] (* or *) Drop[With[{nn = 30}, CoefficientList[Series[x^4*(1 + x + x^2)/(6*(1 - x)^2), {x, 0, nn}], x]*Range[0, nn]!], 4] (* G. C. Greubel, Feb 16 2018 *)
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PROG
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(PARI) x='x+O('x^30); Vec(serlaplace(x^4*(1+x+x^2)/(6*(1-x)^2))) \\ G. C. Greubel, Feb 16 2018
(Magma) [4] cat [Factorial(n)*(n-4)/2: n in [5..30]]; // G. C. Greubel, Feb 16 2018
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CROSSREFS
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KEYWORD
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nonn,easy
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AUTHOR
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STATUS
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approved
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