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A128416
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Expansion of (1-4x^2)/(1+4x+3x^2).
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2
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1, -4, 9, -24, 69, -204, 609, -1824, 5469, -16404, 49209, -147624, 442869, -1328604, 3985809, -11957424, 35872269, -107616804, 322850409, -968551224, 2905653669, -8716961004, 26150883009, -78452649024, 235357947069, -706073841204, 2118221523609
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OFFSET
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0,2
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COMMENTS
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Diagonal sums of number triangle A128414.
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LINKS
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FORMULA
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G.f.: (1-4*x^2)/(1+4*x+3*x^2).
For n > 1, |a(n)| = 3*(|a(n-1)| - 1). - Tamas Kalmar-Nagy (integers(AT)kalmarnagy.com), Sep 17 2010
a(n) = (-1)^n*(9+5*3^n)/6 for n>0.
a(n) = -4*a(n-1)-3*a(n-2) for n>2. (End)
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PROG
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(PARI) Vec((1-4*x^2)/(1+4*x+3*x^2) + O(x^30)) \\ Colin Barker, Sep 21 2016
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CROSSREFS
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KEYWORD
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easy,sign
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AUTHOR
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STATUS
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approved
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