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A146311
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a(n) = cos(2*n*arcsin(sqrt(3))) = (-1)^n*cosh(2*n*arcsinh(sqrt(2))).
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25
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1, -5, 49, -485, 4801, -47525, 470449, -4656965, 46099201, -456335045, 4517251249, -44716177445, 442644523201, -4381729054565, 43374646022449, -429364731169925, 4250272665676801, -42073361925598085, 416483346590304049
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OFFSET
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0,2
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COMMENTS
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Apart from sign, same as A001079 (see first formula).
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LINKS
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FORMULA
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a(n) = ((-5-2*sqrt(6))^n + (-5+2*sqrt(6))^n)/2.
a(n) = -10*a(n-1)-a(n-2).
G.f.: (5*x+1) / (x^2+10*x+1).
(End)
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MATHEMATICA
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Table[Round[N[Cos[2 n ArcSin[Sqrt[3]]], 50]], {n, 0, 100}]
CoefficientList[Series[(5*x + 1)/(x^2 + 10*x + 1), {x, 0, 50}], x] (* G. C. Greubel, Jul 02 2017 *)
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PROG
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(PARI) Vec((5*x+1)/(x^2+10*x+1) + O(x^100)) \\ Colin Barker, Oct 26 2014
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CROSSREFS
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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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