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 A125725 Numbers whose base-7 representation is 222....2. 2
 0, 2, 16, 114, 800, 5602, 39216, 274514, 1921600, 13451202, 94158416, 659108914, 4613762400, 32296336802, 226074357616, 1582520503314, 11077643523200, 77543504662402, 542804532636816, 3799631728457714, 26597422099204000 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 LINKS Davis Smith, Table of n, a(n) for n = 1..1000 Index entries for linear recurrences with constant coefficients, signature (8,-7). FORMULA a(n) = (7^(n-1) - 1)/3 = 2*A023000(n-1). a(n) = 7*a(n-1) + 2, with a(1)=0. - Vincenzo Librandi, Sep 30 2010 G.f.: 2*x^2 / ( (1-x)*(1-7*x) ). - R. J. Mathar, Sep 30 2013 From Davis Smith, Apr 04 2019: (Start) A007310(a(n) + 1) = 7^(n - 1). A047522(a(n + 1)) = -1*A165759(n). (End) EXAMPLE 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. MAPLE seq(2*(7^n-1)/6, n=0..25); MATHEMATICA FromDigits[#, 7]&/@Table[PadLeft[{2}, n, 2], {n, 0, 25}]  (* Harvey P. Dale, Apr 13 2011 *) (7^(Range[25]-1) - 1)/3 (* G. C. Greubel, May 23 2019 *) PROG (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 (MAGMA) [(7^(n-1)-1)/3: n in [1..25]]; // 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 CROSSREFS Cf. A007310, A023000, A047522, A165759. Cf. also A002276, A005610, A020988, A024023, A125831, A125835, A125857 for related or similarly constructed sequences. Sequence in context: A288971 A288970 A037564 * A288965 A207420 A207736 Adjacent sequences:  A125722 A125723 A125724 * A125726 A125727 A125728 KEYWORD easy,nonn,base AUTHOR Zerinvary Lajos, Feb 02 2007 EXTENSIONS Offset corrected by N. J. A. Sloane, Oct 02 2010 STATUS approved

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Last modified May 9 07:33 EDT 2021. Contains 343692 sequences. (Running on oeis4.)