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A339252
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a(0) = 1, a(1) = 4, a(2) = 11, and a(n) = 4*a(n-1) - 4*a(n-2) for n >= 3.
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3
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1, 4, 11, 28, 68, 160, 368, 832, 1856, 4096, 8960, 19456, 41984, 90112, 192512, 409600, 868352, 1835008, 3866624, 8126464, 17039360, 35651584, 74448896, 155189248, 322961408, 671088640, 1392508928, 2885681152, 5972688896, 12348030976, 25501368320, 52613349376
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OFFSET
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0,2
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LINKS
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FORMULA
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G.f.: (1 - x^2)/(1 - 2*x)^2.
a(n) = 2^(n-2)*(3*n + 5) for n >= 1. - Kevin Ryde, Nov 28 2020
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MAPLE
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a := proc(n) option remember; if n <= 2 then return [1, 4, 11][n+1] fi;
4*a(n - 1) - 4*a(n - 2) end: seq(a(n), n = 0..31);
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MATHEMATICA
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CoefficientList[Series[(1 - x^2)/(1 - 2*x)^2, {x, 0, 50}], x]
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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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