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A289077
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a(n) = 2*a(n-1) + a(n-2) - 4*a(n-3) + 2*a(n-4) + a(n-5) -2*a(n-6) + a(n-7) for n >= 7, a(0) = 2, a(1) = 4, a(2) = 7, a(3) = 11, a(4) = 18, a(5) = 30, a(6) = 47.
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2
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2, 4, 7, 11, 18, 30, 47, 74, 114, 176, 269, 411, 625, 950, 1441, 2185, 3310, 5013, 7589, 11487, 17384, 26306, 39804, 60225, 91120, 137860, 208573, 315552, 477400, 722254, 1092691, 1653113, 2500967, 3783660, 5724223, 8660047, 13101596, 19821099, 29986891
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OFFSET
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0,1
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COMMENTS
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Conjecture: a(n) is the number of letters (0's and 1's) in the n-th iterate of the mapping 00->0010, 01->011, 10->100, starting with 00; see A289057.
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LINKS
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FORMULA
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a(n) = 2*a(n-1) + a(n-2) - 4*a(n-3) + 2*a(n-4) + a(n-5) -2*a(n-6) + a(n-7) for n >= 7, a(0) = 2, a(1) = 4, a(2) = 7, a(3) = 11, a(4) = 18, a(5) = 30, a(6) = 47.
G.f.: (-2 + 3*x^2 - x^3 - x^4 - x^5 + x^6 + x^7 - 2*x^8 + x^9)/((-1 + x)^2*(-1 + 2*x^2 + x^5)).
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MATHEMATICA
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Join[{2, 4, 7}, LinearRecurrence[{2, 1, -4, 2, 1, -2, 1}, {11, 18, 30, 47, 74, 114, 176}, 40]]
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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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