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A170955
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a(n) = 10^n - 9.
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6
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1, 91, 991, 9991, 99991, 999991, 9999991, 99999991, 999999991, 9999999991, 99999999991, 999999999991, 9999999999991, 99999999999991, 999999999999991, 9999999999999991, 99999999999999991, 999999999999999991
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OFFSET
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1,2
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COMMENTS
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Column 10 of A193871. - Omar E. Pol, Aug 22 2011
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LINKS
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Vincenzo Librandi, Table of n, a(n) for n = 1..100
Index entries for linear recurrences with constant coefficients, signature (11,-10).
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FORMULA
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a(n) = 10*a(n-1) + 81 for n>1, a(1)=1.
G.f.: x*(1+80*x) / ( (10*x-1)*(x-1) ). - R. J. Mathar, Aug 24 2011
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MATHEMATICA
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CoefficientList[Series[(1 + 80*x)/(1 - 11*x + 10*x^2), {x, 0, 30}], x] (* Vincenzo Librandi, Feb 06 2013 *)
LinearRecurrence[{11, -10}, {1, 91}, 20] (* Harvey P. Dale, Aug 20 2015 *)
10^Range[1, 25] - 9 (* Vincenzo Librandi, Jan 03 2016 *)
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PROG
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(Magma) [10^n-9: n in [1..30]]; // Vincenzo Librandi, Feb 06 2013
(PARI) a(n)=10^n-9 \\ Charles R Greathouse IV, Oct 07 2015
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CROSSREFS
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Cf. A093177.
Sequence in context: A254519 A185375 A036526 * A020316 A221815 A195221
Adjacent sequences: A170952 A170953 A170954 * A170956 A170957 A170958
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KEYWORD
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nonn,easy
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AUTHOR
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Vincenzo Librandi, Feb 26 2010
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EXTENSIONS
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Typo in formula corrected by Jon E. Schoenfield, Jun 19 2010
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STATUS
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approved
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