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A075193
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Expansion of (1-2*x)/(1+x-x^2).
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5
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1, -3, 4, -7, 11, -18, 29, -47, 76, -123, 199, -322, 521, -843, 1364, -2207, 3571, -5778, 9349, -15127, 24476, -39603, 64079, -103682, 167761, -271443, 439204, -710647, 1149851, -1860498, 3010349, -4870847, 7881196, -12752043, 20633239, -33385282, 54018521, -87403803, 141422324
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OFFSET
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0,2
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COMMENTS
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"Inverted" Lucas numbers:
The g.f. is obtained inserting 1/x into the g.f. of Lucas sequence and dividing by x. The closed form is a(n)=(-1)^n*a^(n+1)+(-1)^n*b^(n+1), where a=golden ratio and b=1-a, so that a(n)=(-1)^n*L(n+1), L(n)=Lucas numbers.
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LINKS
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FORMULA
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a(n) = -a(n-1)+a(n-2), a(0)=1, a(1)=-3.
a(n) = term (1,1) in the 1x2 matrix [1,-2] * [-1,1; 1,0]^n. - Alois P. Heinz, Jul 31 2008
E.g.f.: exp(-(1+sqrt(5))*x/2)*(3 + sqrt(5) - 2*exp(sqrt(5)*x))/(1 + sqrt(5)). - Stefano Spezia, Jan 12 2020
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MAPLE
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a:= n-> (Matrix([[1, -2]]). Matrix([[-1, 1], [1, 0]])^(n))[1, 1]:
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MATHEMATICA
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CoefficientList[Series[(1 - 2z)/(1 + z - z^2), {z, 0, 40}], z]
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PROG
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(Haskell)
a075193 n = a075193_list !! n
a075193_list = 1 : -3 : zipWith (-) a075193_list (tail a075193_list)
(Magma) R<x>:=PowerSeriesRing(Integers(), 40); Coefficients(R!( (1-2*x)/(1+x-x^2))); // Marius A. Burtea, Jan 12 2020
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CROSSREFS
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KEYWORD
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easy,sign
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AUTHOR
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Mario Catalani (mario.catalani(AT)unito.it), Sep 07 2002
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STATUS
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approved
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