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A095897
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Expansion of x*(1+4*x-4*x^2)/((1+2*x)*(1-6*x)*(1-8*x^2)).
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5
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1, 8, 48, 320, 1888, 11648, 69504, 419840, 2515456, 15116288, 90667008, 544194560, 3264913408, 19591036928, 117544157184, 705277460480, 4231648116736, 25389989101568, 152339800915968, 914039609753600, 5484236586876928
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OFFSET
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1,2
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LINKS
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FORMULA
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a(n) = 4*a(n-1) + 20*a(n-2) - 32*a(n-3) - 96*a(n-4) for n > 4.
G.f.: x*(1+4*x-4*x^2)/((1+2*x)*(1-6*x)*(1-8*x^2)).
a(n) = 2^(n-2)*(3^n-1+((-1)^n-1)*(sqrt(2)^(n-1)-1)).
a(2k+1) = 2^(2k-1)*(3*9^k-2*2^k+1), a(2k) = 4^(k-1)*(9^k-1). (End)
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MATHEMATICA
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LinearRecurrence[{4, 20, -32, -96}, {1, 8, 48, 320}, 30] (* Harvey P. Dale, Jun 11 2011 *)
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PROG
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(Magma) [Floor(2^(n-2)*(3^n-1+((-1)^n-1)*(Sqrt(2)^(n-1)-1))): n in [1..30]]; // Vincenzo Librandi, Aug 05 2011
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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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EXTENSIONS
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STATUS
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approved
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