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A234272
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G.f.: (1+4*x+x^2)/(1-4*x+x^2).
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1
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1, 8, 32, 120, 448, 1672, 6240, 23288, 86912, 324360, 1210528, 4517752, 16860480, 62924168, 234836192, 876420600, 3270846208, 12206964232, 45557010720, 170021078648, 634527303872, 2368088136840, 8837825243488, 32983212837112, 123095026104960, 459396891582728, 1714492540225952, 6398573269321080
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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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a(n) = 4*a(n-1)-a(n-2) for n>2.
a(n) = 4*(-(2-sqrt(3))^n+(2+sqrt(3))^n)/sqrt(3) for n>1.
(End)
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MATHEMATICA
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CoefficientList[Series[(1+4x+x^2)/(1-4x+x^2), {x, 0, 30}], x] (* or *) LinearRecurrence[{4, -1}, {1, 8, 32}, 30] (* Harvey P. Dale, Jul 12 2015 *)
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PROG
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(PARI) Vec((1+4*x+x^2)/(1-4*x+x^2) + O(x^40)) \\ Colin Barker, Oct 12 2015
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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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