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A052954
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Expansion of (2-x-x^2-x^3)/((1-x)*(1-x^2-x^3)).
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1
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2, 1, 2, 2, 2, 3, 3, 4, 5, 6, 8, 10, 13, 17, 22, 29, 38, 50, 66, 87, 115, 152, 201, 266, 352, 466, 617, 817, 1082, 1433, 1898, 2514, 3330, 4411, 5843, 7740, 10253, 13582, 17992, 23834, 31573, 41825, 55406, 73397, 97230, 128802, 170626, 226031, 299427
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OFFSET
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0,1
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COMMENTS
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For n > 2, a(n) = floor(sqrt(a(n-3)*a(n-2) + a(n-2)*a(n-1) + a(n-1)*a(n-3))). - Gerald McGarvey, Sep 19 2004
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LINKS
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FORMULA
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G.f.: (2-x-x^2-x^3)/((1-x)*(1-x^2-x^3)).
a(n) = a(n-2) + a(n-3) - 1.
a(n) = 1 + Sum_{alpha=RootOf(-1+z^2+z^3)} (1/23)*(3 +7*alpha -2*alpha^2) * alpha^(-1-n).
lim n->inf a(n)/a(n-1) = positive root of 1+x-x^3 (smallest Pisot-Vijayaraghavan number, A060006) - Gerald McGarvey, Sep 19 2004
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MAPLE
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spec:= [S, {S=Union(Sequence(Prod(Union(Prod(Z, Z), Z), Z)), Sequence(Z))}, unlabeled ]: seq(combstruct[count ](spec, size=n), n=0..20);
seq(coeff(series((2-x-x^2-x^3)/((1-x)*(1-x^2-x^3)), x, n+1), x, n), n = 0 .. 40); # G. C. Greubel, Oct 22 2019
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MATHEMATICA
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LinearRecurrence[{1, 1, 0, -1}, {2, 1, 2, 2}, 40] (* G. C. Greubel, Oct 22 2019 *)
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PROG
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(PARI) my(x='x+O('x^40)); Vec((2-x-x^2-x^3)/((1-x)*(1-x^2-x^3))) \\ G. C. Greubel, Oct 22 2019
(Magma) R<x>:=PowerSeriesRing(Integers(), 40); Coefficients(R!( (2-x-x^2-x^3)/((1-x)*(1-x^2-x^3)) )); // G. C. Greubel, Oct 22 2019
(Sage)
P.<x> = PowerSeriesRing(ZZ, prec)
return P((2-x-x^2-x^3)/((1-x)*(1-x^2-x^3))).list()
(GAP) a:=[2, 1, 2, 2];; for n in [5..40] do a[n]:=a[n-1]+a[n-2]-a[n-4]; od; a; # G. C. Greubel, Oct 22 2019
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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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encyclopedia(AT)pommard.inria.fr, Jan 25 2000
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EXTENSIONS
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STATUS
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approved
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