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A115341
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a(n) = abs(A154879(n+1)).
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17
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2, 4, 0, 8, 8, 24, 40, 88, 168, 344, 680, 1368, 2728, 5464, 10920, 21848, 43688, 87384, 174760, 349528, 699048, 1398104, 2796200, 5592408, 11184808, 22369624, 44739240, 89478488, 178956968, 357913944, 715827880, 1431655768, 2863311528
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OFFSET
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0,1
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COMMENTS
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For n>=1, a(n) is a(n) is the number of generalized compositions of n+3 when there are i^2-2*i-1 different types of i, (i=1,2,...). - Milan Janjic, Sep 24 2010
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LINKS
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FORMULA
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a(n) = (2^(n+1)-8*(-1)^n)/3, n>0.
a(n) = a(n-1) + 2*a(n-2), n>2.
G.f.: 2+4*x*(1-x)/((1+x)*(1-2*x)).
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MATHEMATICA
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g0[n_] = 2 - Sum[(-1)^(i + 1)/Sqrt[2]^(2*i), {i, 0, n}] f[x_] = ZTransform[g0[n], n, x] g[n_] = InverseZTransform[f[1/x], x, n] a0 = Table[Abs[g[n]], {n, 1, 25}]
Table[If[n==0, 2, (2^(n+1)-8*(-1)^n)/3], {n, 0, 30}] (* G. C. Greubel, Dec 30 2017 *)
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PROG
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(PARI) for(n=0, 30, print1(if(n==0, 2, (2^(n+1)-8*(-1)^n)/3), ", ")) \\ G. C. Greubel, Dec 30 2017
(Magma) [2] cat [(2^(n+1)-8*(-1)^n)/3: n in [1..30]]; // G. C. Greubel, Dec 30 2017
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CROSSREFS
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KEYWORD
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nonn,easy,less
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AUTHOR
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EXTENSIONS
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Edited by the Associate Editors of the OEIS, Aug 21 2009
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STATUS
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approved
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