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A136412
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a(n) = (5*4^n + 1)/3.
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11
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2, 7, 27, 107, 427, 1707, 6827, 27307, 109227, 436907, 1747627, 6990507, 27962027, 111848107, 447392427, 1789569707, 7158278827, 28633115307, 114532461227, 458129844907, 1832519379627, 7330077518507, 29320310074027
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OFFSET
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0,1
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COMMENTS
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An Engel expansion of 4/5 to the base b := 4/3 as defined in A181565, with the associated series expansion 4/5 = b/2 + b^2/(2*7) + b^3/(2*7*27) + b^4/(2*7*27*107) + .... Cf. A199115 and A140660. - Peter Bala, Oct 29 2013
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LINKS
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FORMULA
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a(n) = 4*a(n-1) - 1.
O.g.f.: (2-3*x)/((1-x)*(1-4*x)). - R. J. Mathar, Apr 04 2008
E.g.f.: (1/3)*(5*exp(4*x) + exp(x)). - G. C. Greubel, Jan 19 2023
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MATHEMATICA
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LinearRecurrence[{5, -4}, {2, 7}, 31] (* G. C. Greubel, Jan 19 2023 *)
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PROG
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(Haskell)
a136412 = (`div` 3) . (+ 1) . (* 5) . (4 ^)
(SageMath) [(5*4^n+1)/3 for n in range(31)] # G. C. Greubel, Jan 19 2023
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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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EXTENSIONS
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Formula in definition and more terms from R. J. Mathar, Apr 04 2008
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STATUS
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approved
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