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A099842
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Expansion of (1-x)/(1 + 6*x - 3*x^2).
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5
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1, -7, 45, -291, 1881, -12159, 78597, -508059, 3284145, -21229047, 137226717, -887047443, 5733964809, -37064931183, 239591481525, -1548743682699, 10011236540769, -64713650292711, 418315611378573, -2704034619149571, 17479154549033145, -112987031151647583
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OFFSET
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0,2
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COMMENTS
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A transformation of x/(1-2*x-2*x^2).
The g.f. is the transform of the g.f. of A002605 under the mapping G(x) -> (-1/(1+x))*G((x-1)/(x+1)). In general this mapping transforms x/(1-k*x-k*x^2) into (1-x)/(1+2*(k+1)*x-(2*k-1)*x^2).
For n >= 1, |a(n)| equals the numbers of words of length n-1 on alphabet {0,1,...,6} containing no subwords 00, 11, 22, 33. - Milan Janjic, Jan 31 2015
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LINKS
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FORMULA
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G.f.: (1-x)/(1+6*x-3*x^2).
a(n) = (1/2 - sqrt(3)/3)*(-3 + 2*sqrt(3))^n + (1/2 + sqrt(3)/3)*(-3 - 2*sqrt(3))^n.
a(n) = (-1)^n*Sum_{k=0..n} binomial(n, k)(-1)^(n-k)*A002605(2k+2)/2.
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MATHEMATICA
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LinearRecurrence[{-6, 3}, {1, -7}, 31] (* G. C. Greubel, Oct 10 2022 *)
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PROG
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(Magma) [n le 2 select (-7)^(n-1) else -6*Self(n-1) +3*Self(n-2): n in [1..31]]; // G. C. Greubel, Oct 10 2022
(SageMath)
A099842 = BinaryRecurrenceSequence(-6, 3, 1, -7)
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CROSSREFS
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KEYWORD
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easy,sign
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AUTHOR
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STATUS
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approved
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