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A125725
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Numbers whose base-7 representation is 222....2.
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2
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0, 2, 16, 114, 800, 5602, 39216, 274514, 1921600, 13451202, 94158416, 659108914, 4613762400, 32296336802, 226074357616, 1582520503314, 11077643523200, 77543504662402, 542804532636816, 3799631728457714, 26597422099204000
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OFFSET
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1,2
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LINKS
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FORMULA
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a(n) = (7^(n-1) - 1)/3 = 2*A023000(n-1).
G.f.: 2*x^2 / ( (1-x)*(1-7*x) ). - R. J. Mathar, Sep 30 2013
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EXAMPLE
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base 7.......decimal
0..................0
2..................2
22................16
222..............114
2222.............800
22222...........5602
222222.........39216
2222222.......274514
22222222.....1921600
222222222...13451202
etc...........etc.
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MAPLE
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seq(2*(7^n-1)/6, n=0..25);
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MATHEMATICA
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FromDigits[#, 7]&/@Table[PadLeft[{2}, n, 2], {n, 0, 25}] (* Harvey P. Dale, Apr 13 2011 *)
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PROG
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(PARI) vector(25, n, (7^(n-1)-1)/3) \\ Davis Smith, Apr 04 2019
(Magma) [0] cat [n:n in [1..15000000]| Set(Intseq(n, 7)) subset [2]]; // Marius A. Burtea, May 06 2019
(Sage) [(7^(n-1) -1)/3 for n in (1..25)] # G. C. Greubel, May 23 2019
(GAP) List([1..25], n-> (7^(n-1) -1)/3) # G. C. Greubel, May 23 2019
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CROSSREFS
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KEYWORD
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easy,nonn,base
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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