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A057091
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Scaled Chebyshev U-polynomials evaluated at i*sqrt(2). Generalized Fibonacci sequence.
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12
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1, 8, 72, 640, 5696, 50688, 451072, 4014080, 35721216, 317882368, 2828828672, 25173688320, 224020135936, 1993550594048, 17740565839872, 157872931471360, 1404907978489856, 12502247279689728, 111257242065436672, 990075914761011200, 8810665254611582976
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OFFSET
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0,2
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COMMENTS
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a(n) gives the length of the word obtained after n steps with the substitution rule 0->1^8, 1->(1^8)0, starting from 0. The number of 1's and 0's of this word is 8*a(n-1) and 8*a(n-2), resp.
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LINKS
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FORMULA
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a(n) = 8*(a(n-1) + a(n-2)), a(-1)=0, a(0)=1.
a(n) = S(n, i*2*sqrt(2))*(-i*2*sqrt(2))^n with S(n, x) := U(n, x/2), Chebyshev's polynomials of the 2nd kind, A049310.
G.f.: 1/(1 - 8*x - 8*x^2).
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MATHEMATICA
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LinearRecurrence[{8, 8}, {1, 8}, 50] (* G. C. Greubel, Jan 24 2018 *)
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PROG
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(Sage) [lucas_number1(n, 8, -8) for n in range(0, 20)] # Zerinvary Lajos, Apr 25 2009
(PARI) Vec(1/(1-8*x-8*x^2) + O(x^30)) \\ Colin Barker, Jun 14 2015
(Magma) I:=[1, 8]; [n le 2 select I[n] else 8*Self(n-1) + 8*Self(n-2): n in [1..30]]; // G. C. Greubel, Jan 24 2018
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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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