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%I #31 Sep 08 2022 08:45:49
%S 1,91,991,9991,99991,999991,9999991,99999991,999999991,9999999991,
%T 99999999991,999999999991,9999999999991,99999999999991,
%U 999999999999991,9999999999999991,99999999999999991,999999999999999991
%N a(n) = 10^n - 9.
%C Column 10 of A193871. - _Omar E. Pol_, Aug 22 2011
%H Vincenzo Librandi, <a href="/A170955/b170955.txt">Table of n, a(n) for n = 1..100</a>
%H <a href="/index/Rec#order_02">Index entries for linear recurrences with constant coefficients</a>, signature (11,-10).
%F a(n) = 10*a(n-1) + 81 for n>1, a(1)=1.
%F G.f.: x*(1+80*x) / ( (10*x-1)*(x-1) ). - _R. J. Mathar_, Aug 24 2011
%t CoefficientList[Series[(1 + 80*x)/(1 - 11*x + 10*x^2), {x, 0, 30}], x] (* _Vincenzo Librandi_, Feb 06 2013 *)
%t LinearRecurrence[{11,-10},{1,91},20] (* _Harvey P. Dale_, Aug 20 2015 *)
%t 10^Range[1, 25] - 9 (* _Vincenzo Librandi_, Jan 03 2016 *)
%o (Magma) [10^n-9: n in [1..30]]; // _Vincenzo Librandi_, Feb 06 2013
%o (PARI) a(n)=10^n-9 \\ _Charles R Greathouse IV_, Oct 07 2015
%Y Cf. A093177.
%K nonn,easy
%O 1,2
%A _Vincenzo Librandi_, Feb 26 2010
%E Typo in formula corrected by _Jon E. Schoenfield_, Jun 19 2010
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