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A233828
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a(n) = 2*a(n-1) + 2*a(n-2) + a(n-3). a(0) = -1, a(1) = 1, a(2) = 1.
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3
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-1, 1, 1, 3, 9, 25, 71, 201, 569, 1611, 4561, 12913, 36559, 103505, 293041, 829651, 2348889, 6650121, 18827671, 53304473, 150914409, 427265435, 1209664161, 3424773601, 9696140959, 27451493281, 77720042081, 220039211683, 622970000809, 1763738467065
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OFFSET
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0,4
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LINKS
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FORMULA
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G.f.: (-1 + 3*x + x^2) / (1 - 2*x - 2*x^2 - x^3).
a(n) - a(n-1) = -2 * (-1)^n * A078054(n-3).
a(n)^2 - a(n-1) * a(n+1) = -2 * (-1)^n * A078004(n-1).
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EXAMPLE
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G.f. = -1 + x + x^2 + 3*x^3 + 9*x^4 + 25*x^5 + 71*x^6 + 201*x^7 + 569*x^8 + ...
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MATHEMATICA
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CoefficientList[Series[(-1+3*x+x^2)/(1-2*x-2*x^2-x^3), {x, 0, 50}], x] (* G. C. Greubel, Aug 07 2018 *)
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PROG
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(PARI) {a(n) = if( n<0, polcoeff( (-1 -x + x^2) / (1 + 2*x + 2*x^2 - x^3) + x * O(x^-n), -n), polcoeff( (-1 + 3*x + x^2) / (1 - 2*x - 2*x^2 - x^3) + x * O(x^n), n))}
(Magma) m:=50; R<x>:=PowerSeriesRing(Integers(), m); Coefficients(R!((-1+3*x+x^2)/(1-2*x-2*x^2-x^3))); // G. C. Greubel, Aug 07 2018
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CROSSREFS
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KEYWORD
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sign
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AUTHOR
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STATUS
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approved
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