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A167030
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a(n) = (2^n - (-1)^n - 3)/3.
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7
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-1, 0, 0, 2, 4, 10, 20, 42, 84, 170, 340, 682, 1364, 2730, 5460, 10922, 21844, 43690, 87380, 174762, 349524, 699050, 1398100, 2796202, 5592404, 11184810, 22369620, 44739242, 89478484, 178956970, 357913940, 715827882
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OFFSET
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0,4
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LINKS
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FORMULA
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a(n) = 2*a(n-1) + a(n-2) - 2*a(n-3).
G.f.: (1 - 2*x - x^2)/((x^2 - 1)*(1-2*x)).
a(2n+2) = a(2n) + 2^(2n).
E.g.f.: (1/3)*(exp(2*x) - 3*exp(x) - exp(-x)). - G. C. Greubel, May 30 2016
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MATHEMATICA
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f[n_] := (2^n - (-1)^n - 3)/3; Array[f, 32, 0]
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PROG
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CROSSREFS
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A026644 is an essentially identical sequence.
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KEYWORD
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sign,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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