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 A198971 5*10^n-1. 6
 4, 49, 499, 4999, 49999, 499999, 4999999, 49999999, 499999999, 4999999999, 49999999999, 499999999999, 4999999999999, 49999999999999, 499999999999999, 4999999999999999, 49999999999999999, 499999999999999999, 4999999999999999999 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,1 COMMENTS Also maximal value of GCD of 2 distinct (n+1)-digit numbers (compare with A126687). - Michel Marcus, Jun 24 2013 LINKS Vincenzo Librandi, Table of n, a(n) for n = 0..200 Index entries for linear recurrences with constant coefficients, signature (11,-10). FORMULA a(n) = 10*a(n-1)+9. a(n) = 11*a(n-1)-10*a(n-2), n>1. G.f.: (4 + 5*x)/(1 - 11*x + 10*x^2). - Vincenzo Librandi, Jan 03 2013 MATHEMATICA CoefficientList[Series[(4 + 5*x)/(1 - 11*x + 10*x^2), {x, 0, 30}], x] (* Vincenzo Librandi, Jan 03 2013 *) LinearRecurrence[{11, -10}, {4, 49}, 20] (* Harvey P. Dale, Dec 30 2018 *) PROG (MAGMA) [5*10^n-1 : n in [0..20]] (PARI) a(n)=5*10^n-1 \\ Charles R Greathouse IV, Oct 07 2015 CROSSREFS Sequence in context: A067474 A053769 A173038 * A273230 A199028 A189146 Adjacent sequences:  A198968 A198969 A198970 * A198972 A198973 A198974 KEYWORD nonn,easy AUTHOR Vincenzo Librandi, Nov 02 2011 STATUS approved

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Last modified February 19 18:30 EST 2019. Contains 320327 sequences. (Running on oeis4.)