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A228207
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x-values in the solution to x^2 - 20y^2 = 176.
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2
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14, 16, 26, 34, 64, 86, 166, 224, 434, 586, 1136, 1534, 2974, 4016, 7786, 10514, 20384, 27526, 53366, 72064, 139714, 188666, 365776, 493934, 957614, 1293136, 2507066, 3385474, 6563584, 8863286, 17183686, 23204384, 44987474, 60749866, 117778736, 159045214
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OFFSET
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1,1
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LINKS
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FORMULA
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G.f.: -2*x*(x-1)*(7*x^2+15*x+7) / ((x^2-x-1)*(x^2+x-1)).
a(n) = 3*a(n-2)-a(n-4).
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MATHEMATICA
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CoefficientList[Series[-2 (x - 1) (7 x^2 + 15 x + 7) / ((x^2 - x - 1) (x^2 + x - 1)), {x, 0, 40}], x] (* Vincenzo Librandi, Aug 17 2013 *)
LinearRecurrence[{0, 3, 0, -1}, {14, 16, 26, 34}, 50] (* Harvey P. Dale, May 25 2023 *)
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PROG
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(PARI) Vec(-2*x*(x-1)*(7*x^2+15*x+7)/((x^2-x-1)*(x^2+x-1)) + O(x^100))
(Magma) I:=[14, 16, 26, 34]; [n le 4 select I[n] else 3*Self(n-2)-Self(n-4): n in [1..40]]; // Vincenzo Librandi, Aug 17 2013 *)
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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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