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A087800
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a(n) = 12*a(n-1) - a(n-2), with a(0) = 2 and a(1) = 12.
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4
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2, 12, 142, 1692, 20162, 240252, 2862862, 34114092, 406506242, 4843960812, 57721023502, 687808321212, 8195978831042, 97663937651292, 1163771272984462, 13867591338162252, 165247324784962562, 1969100306081388492
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OFFSET
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0,1
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COMMENTS
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a(n+1)/a(n) converges to (6+sqrt(35)) = 11.9160797... a(0)/a(1)=2/12; a(1)/a(2)=12/142; a(2)/a(3)=142/1692; a(3)/a(4)=1692/20162; ... etc. Lim_{n->infinity} a(n)/a(n+1) = 0.0839202... = 1/(6+sqrt(35)) = (6-sqrt(35)).
Except for the first term, positive values of x (or y) satisfying x^2 - 12xy + y^2 + 140 = 0. - Colin Barker, Feb 25 2014
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LINKS
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FORMULA
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a(n) = (6+sqrt(35))^n + (6-sqrt(35))^n.
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EXAMPLE
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a(4) = 20162 = 12a(3) - a(2) = 12*1692 - 142 = (6+sqrt(35))^4 + (6-sqrt(35))^4 = 20161.9999504 + 0.00004959 = 20162.
G.f. = 2 + 12*x + 142*x^2 + 1692*x^3 + 20162*x^4 + 240252*x^5 + ...
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MATHEMATICA
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a[0] = 2; a[1] = 12; a[n_] := 12a[n - 1] - a[n - 2]; Table[ a[n], {n, 0, 17}] (* Robert G. Wilson v, Jan 30 2004 *)
CoefficientList[Series[(2 - 12 x)/(1 - 12 x + x^2), {x, 0, 40}], x] (* Vincenzo Librandi, Feb 28 2014 *)
LinearRecurrence[{12, -1}, {2, 12}, 20] (* Harvey P. Dale, Jan 29 2019 *)
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PROG
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(Sage) [lucas_number2(n, 12, 1) for n in range(1, 20)] # Zerinvary Lajos, Jun 25 2008
(PARI) Vec((2-12*x)/(1-12*x+x^2) + O(x^100)) \\ Colin Barker, Feb 25 2014
(PARI) {a(n) = 2 * polchebyshev( n, 1, 6)}; /* Michael Somos, May 28 2014 */
(Magma) I:=[2, 12]; [n le 2 select I[n] else 12*Self(n-1) - Self(n-2): n in [1..30]]; // G. C. Greubel, Nov 07 2018
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CROSSREFS
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KEYWORD
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easy,nonn
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AUTHOR
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Nikolay V. Kosinov (kosinov(AT)unitron.com.ua), Oct 11 2003
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STATUS
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approved
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