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A078484
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G.f.: -x*(1-2*x+2*x^2)/(2*x^3-4*x^2+4*x-1).
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3
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0, 1, 2, 6, 18, 52, 148, 420, 1192, 3384, 9608, 27280, 77456, 219920, 624416, 1772896, 5033760, 14292288, 40579904, 115217984, 327136896, 928835456, 2637230208, 7487852800, 21260161280, 60363694336, 171389837824, 486624896512, 1381667623424, 3922950583296
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OFFSET
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0,3
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COMMENTS
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Enumerates pop-stacks.
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LINKS
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FORMULA
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a(0)=0, a(1)=1, a(2)=2, a(3)=6, a(n) = 4*a(n-1)-4*a(n-2)+2*a(n-3). - Harvey P. Dale, Jul 21 2012
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MATHEMATICA
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CoefficientList[Series[-x(1-2x+2x^2)/(2x^3-4x^2+4x-1), {x, 0, 30}], x] (* or *) Join[{0}, LinearRecurrence[{4, -4, 2}, {1, 2, 6}, 30]] (* Harvey P. Dale, Jul 21 2012 *)
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CROSSREFS
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KEYWORD
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nonn
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AUTHOR
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EXTENSIONS
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Replaced definition with g.f. given by Atkinson and Stitt (2002). - N. J. A. Sloane, May 24 2016
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STATUS
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approved
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