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A113655
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Reverse blocks of three in the sequence of natural numbers.
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6
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3, 2, 1, 6, 5, 4, 9, 8, 7, 12, 11, 10, 15, 14, 13, 18, 17, 16, 21, 20, 19, 24, 23, 22, 27, 26, 25, 30, 29, 28, 33, 32, 31, 36, 35, 34, 39, 38, 37, 42, 41, 40, 45, 44, 43, 48, 47, 46, 51, 50, 49, 54, 53, 52, 57, 56, 55, 60, 59, 58, 63, 62, 61, 66, 65, 64, 69, 68, 67, 72, 71, 70
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OFFSET
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1,1
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LINKS
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FORMULA
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G.f.: (3*x - x^2 - x^3 + 2*x^4)/(1 - x - x^3 + x^4) = x*(3 - x - x^2 + 2*x^3)/((1 + x + x^2)*(1-x)^2). - Jaume Oliver Lafont, Mar 25 2009
Sum_{n>=1} (-1)^(n+1)/a(n) = log(2). - Amiram Eldar, Jan 31 2023
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MAPLE
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MATHEMATICA
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f[n_] := Switch[ Mod[n, 3], 0, n - 2, 1, n + 2, 2, n]; Array[f, 72] (* Robert G. Wilson v, Jan 18 2006 *)
LinearRecurrence[{1, 0, 1, -1}, {3, 2, 1, 6}, 100] (* or *) CoefficientList[Series[(3 - x - x^2 + 2 x^3) / ((1 + x + x^2) (1 - x)^2), {x, 0, 80}], x] (* Vincenzo Librandi, Sep 28 2017 *)
Reverse/@Partition[Range[81], 3]//Flatten (* Harvey P. Dale, Oct 11 2020 *)
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PROG
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(Magma) I:=[3, 2, 1, 6]; [n le 4 select I[n] else Self(n-1)+Self(n-3)-Self(n-4): n in [1..80]]; // Vincenzo Librandi, Sep 28 2017
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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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Parag D. Mehta (pmehta23(AT)gmail.com), Jan 16 2006
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EXTENSIONS
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STATUS
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approved
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