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A098574
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a(n) = Sum_{k=0..floor(n/7)} C(n-5*k,2*k).
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3
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1, 1, 1, 1, 1, 1, 1, 2, 4, 7, 11, 16, 22, 29, 38, 51, 71, 102, 149, 218, 316, 452, 639, 897, 1257, 1766, 2493, 3536, 5031, 7165, 10196, 14484, 20538, 29085, 41168, 58282, 82561, 117036, 165995, 235492, 334074, 473824, 671856, 952449, 1350078, 1913702
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OFFSET
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0,8
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LINKS
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G. C. Greubel, Table of n, a(n) for n = 0..1000
R. Austin and R. K. Guy, Binary sequences without isolated ones, Fib. Quart., 16 (1978), 84-86.
V. C. Harris, C. C. Styles, A generalization of Fibonacci numbers, Fib. Quart. 2 (1964) 277-289, sequence u(n,5,2).
Index entries for linear recurrences with constant coefficients, signature (2,-1,0,0,0,0,1).
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FORMULA
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G.f.: (1-x)/(1-2*x+x^2-x^7).
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MATHEMATICA
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CoefficientList[Series[(1-x)/(1-2*x+x^2-x^7), {x, 0, 50}], x] (* G. C. Greubel, Feb 03 2018 *)
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PROG
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(PARI) a(n) = sum(k=0, n\7, binomial(n-5*k, 2*k)); \\ Michel Marcus, Sep 06 2017
(PARI) x='x+O('x^30); Vec((1-x)/(1-2*x+x^2-x^7)) \\ G. C. Greubel, Feb 03 2018
(Magma) Q:=Rationals(); R<x>:=PowerSeriesRing(Q, 40); Coefficients(R!((1-x)/(1-2*x+x^2-x^7))) // G. C. Greubel, Feb 03 2018
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CROSSREFS
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Cf. A005251, A005252, A005253, A005689.
Sequence in context: A212367 A225088 A175777 * A212366 A309838 A334251
Adjacent sequences: A098571 A098572 A098573 * A098575 A098576 A098577
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KEYWORD
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easy,nonn
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AUTHOR
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Paul Barry, Sep 16 2004
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STATUS
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approved
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