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A146005
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a(n) = n*Lucas(n).
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4
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0, 1, 6, 12, 28, 55, 108, 203, 376, 684, 1230, 2189, 3864, 6773, 11802, 20460, 35312, 60707, 104004, 177631, 302540, 513996, 871266, 1473817, 2488368, 4194025, 7057518, 11858508, 19898116, 33345679, 55814940, 93320819, 155867104
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OFFSET
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0,3
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LINKS
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FORMULA
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G.f.: x(1+4x-x^2)/(1-x-x^2)^2.
a(n) = 2*a(n-1)+a(n-2)-2*a(n-3)-a(n-4).
E.g.f.: x*exp(x/2)*(cosh(sqrt(5)*x/2) + sqrt(5)*sinh(sqrt(5)*x/2)). - G. C. Greubel, Jan 30 2016
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MATHEMATICA
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CoefficientList[Series[x * (1 + 4*x - x^2)/(1 - x - x^2)^2, {x, 0, 40}], x] (* Vincenzo Librandi, Dec 13 2012 *)
LinearRecurrence[{2, 1, -2, -1}, {0, 1, 6, 12}, 40] (* Harvey P. Dale, Apr 03 2013 *)
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PROG
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(Magma) I:=[0, 1, 6, 12]; [n le 4 select I[n] else 2*Self(n-1) + Self(n-2) - 2*Self(n-3) - Self(n-4): n in [1..40]]; // Vincenzo Librandi, Dec 13 2012
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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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STATUS
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approved
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