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A015258
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Gaussian binomial coefficient [ n,2 ] for q = -7.
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3
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1, 43, 2150, 105050, 5149551, 252313293, 12363454300, 605808540100, 29684623509101, 1454546516636543, 71272779562356450, 3492366196825305150, 171125943656551078651, 8385171239086224969793, 410873390715818468708600, 20132796145070950850400200
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OFFSET
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2,2
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REFERENCES
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J. Goldman and G.-C. Rota, The number of subspaces of a vector space, pp. 75-83 of W. T. Tutte, editor, Recent Progress in Combinatorics. Academic Press, NY, 1969.
I. P. Goulden and D. M. Jackson, Combinatorial Enumeration. Wiley, NY, 1983, p. 99.
M. Sved, Gaussians and binomials, Ars. Combinatoria, 17A (1984), 325-351.
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LINKS
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FORMULA
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G.f.: x^2/((1-x)*(1+7x)*(1-49x)).
a(n) = (6*(-7)^n - 7 +49^n)/2688. - R. J. Mathar, May 25 2011
a(n) = 43*a(n-1) + 301*a(n-2) - 343*a(n-3), n >= 5. - Harvey P. Dale, May 25 2011
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MATHEMATICA
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CoefficientList[Series[1/((1-x)(1+7x)(1-49x)), {x, 0, 20}], x] (* or *) LinearRecurrence[{43, 301, -343}, {1, 43, 2150}, 20] (* Harvey P. Dale, May 25 2011 *)
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PROG
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(Sage) [gaussian_binomial(n, 2, -7) for n in range(2, 16)] # Zerinvary Lajos, May 27 2009
(Magma) I:=[1, 43, 2150]; [n le 3 select I[n] else 43*Self(n-1) + 301*Self(n-2) - 343*Self(n-3): n in [1..20]]; // Vincenzo Librandi, Oct 27 2012
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CROSSREFS
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KEYWORD
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nonn,easy
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AUTHOR
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STATUS
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approved
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