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 A125835 Numbers whose base-8 or octal representation is 22222222.......2. 5
 0, 2, 18, 146, 1170, 9362, 74898, 599186, 4793490, 38347922, 306783378, 2454267026, 19634136210, 157073089682, 1256584717458, 10052677739666, 80421421917330, 643371375338642, 5146971002709138, 41175768021673106, 329406144173384850, 2635249153387078802, 21081993227096630418 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 LINKS G. C. Greubel, Table of n, a(n) for n = 1..1000 Index entries for linear recurrences with constant coefficients, signature (9,-8). FORMULA a(n) = 2*(8^(n-1) - 1)/7. a(n) = 8*a(n-1) + 2, with a(1)=0. - Vincenzo Librandi, Sep 30 2010 From G. C. Greubel, Aug 03 2019: (Start) a(n) = 2*A023001(n). G.f.: 2*x^2/((1-x)*(1-8*x)). E.g.f.: 2*(exp(8*x) - exp(x))/7. (End) EXAMPLE Octal.............decimal 0.......................0 2.......................2 22.....................18 222...................146 2222.................1170 22222................9362 222222..............74898 2222222............599186 22222222..........4793490 222222222........38347922 2222222222......306783378 etc. ...............etc. MAPLE seq(2*(8^n-1)/7, n=0..30); MATHEMATICA nxt2[n_]:=Module[{idn=IntegerDigits[n, 8]}, FromDigits[PadLeft[idn, Length[idn]+1, 2], 8]]; Join[{0}, NestList[nxt2, 2, 30]] (* Harvey P. Dale, Mar 09 2011 *) Module[{nn=30, c}, c=PadRight[{}, nn, 2]; Table[FromDigits[Take[c, n], 8], {n, 0, nn}]] (* Harvey P. Dale, Sep 05 2015 *) 2*(8^(Range[30]-1) -1)/7 (* G. C. Greubel, Aug 03 2019 *) PROG (PARI) a(n)=2*(1<<(3*n-3)\7) \\ Charles R Greathouse IV, Mar 09 2011 (PARI) vector(30, n, 2*(8^(n-1) -1)/7) \\ G. C. Greubel, Aug 03 2019 (Magma) [2*(8^(n-1) -1)/7: n in [1..30]]; // G. C. Greubel, Aug 03 2019 (Sage) [2*(8^(n-1) -1)/7 for n in (1..30)] # G. C. Greubel, Aug 03 2019 (GAP) List([1..30], n-> 2*(8^(n-1) -1)/7); # G. C. Greubel, Aug 03 2019 CROSSREFS Cf. A023001. Sequence in context: A208654 A037565 A329170 * A356623 A091170 A207319 Adjacent sequences: A125832 A125833 A125834 * A125836 A125837 A125838 KEYWORD easy,nonn AUTHOR Zerinvary Lajos, Feb 03 2007 EXTENSIONS Offset corrected by N. J. A. Sloane, Oct 02 2010 Terms a(21) onward added by G. C. Greubel, Aug 03 2019 STATUS approved

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Last modified June 20 07:26 EDT 2024. Contains 373512 sequences. (Running on oeis4.)