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A248417
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Sum of n-th powers of the roots of x^3 +25* x^2 + 31*x - 1.
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5
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3, -25, 563, -13297, 314947, -7460905, 176745971, -4187046273, 99189570819, -2349764090041, 55665038509363, -1318684086371985, 31239136201419331, -740043533319442377, 17531356426655688179, -415311321997288071457, 9838570957172556010499, -233072091590971314359129, 5521391278779936334581299
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OFFSET
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0,1
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COMMENTS
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a(n) is x1^n + x2^n + x3^n, where x1, x2, x3 are the roots of the polynomial
x^3 +25* x^2 + 31*x - 1.
x1 = (tan(2*Pi/7)*tan(4*Pi/7))/(tan(Pi/7))^2,
x2 = (tan(4*Pi/7)*tan(Pi/7))/(tan(2*Pi/7))^2,
x3 = (tan(Pi/7)*tan(2*Pi/7))(tan(4*Pi/7))^2.
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LINKS
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FORMULA
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a(n) = ((tan(Pi/7))^2/(tan(2*Pi/7)*tan(4*Pi/7)))^(-n)+((tan(2*Pi/7))^2/(tan(4*Pi/7)*tan(Pi/7)))^(-n)+((tan(4*Pi/7))^2/(tan(Pi/7)*tan(2*Pi/7)))^(-n).
a(n) = -25*a(n-1) - 31*a(n-2) + a(n-3).
G.f.: (3+50*x+31*x^2) / (1+25*x+31*x^2-x^3). - Colin Barker, Jul 01 2016
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MATHEMATICA
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CoefficientList[Series[(3 + 50 x + 31 x^2)/(1 + 25 x + 31 x^2 - x^3), {x, 0, 18}], x] (* Michael De Vlieger, Jul 01 2016 *)
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PROG
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(PARI) Vec((3+50*x+31*x^2)/(1+25*x+31*x^2-x^3) + O(x^20)) \\ Colin Barker, Jul 01 2016
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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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STATUS
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approved
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