This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A170955 #37 Sep 07 2024 01:23:43
%S A170955 1,91,991,9991,99991,999991,9999991,99999991,999999991,9999999991,
%T A170955 99999999991,999999999991,9999999999991,99999999999991,
%U A170955 999999999999991,9999999999999991,99999999999999991,999999999999999991,9999999999999999991,99999999999999999991,999999999999999999991
%N A170955 a(n) = 10^n - 9.
%C A170955 Column 10 of A193871. - _Omar E. Pol_, Aug 22 2011
%H A170955 Vincenzo Librandi, <a href="/A170955/b170955.txt">Table of n, a(n) for n = 1..100</a>
%H A170955 <a href="/index/Rec#order_02">Index entries for linear recurrences with constant coefficients</a>, signature (11,-10).
%F A170955 a(n) = 10*a(n-1) + 81 for n > 1, a(1) = 1.
%F A170955 G.f.: x*(1+80*x)/((10*x-1)*(x-1)). - _R. J. Mathar_, Aug 24 2011
%F A170955 From _Elmo R. Oliveira_, Sep 06 2024: (Start)
%F A170955 E.g.f.: 8 + exp(x)*(exp(9*x) - 9).
%F A170955 a(n) = 11*a(n-1) - 10*a(n-2) for n > 2. (End)
%t A170955 CoefficientList[Series[(1 + 80*x)/(1 - 11*x + 10*x^2), {x, 0, 30}], x] (* _Vincenzo Librandi_, Feb 06 2013 *)
%t A170955 LinearRecurrence[{11,-10},{1,91},20] (* _Harvey P. Dale_, Aug 20 2015 *)
%t A170955 10^Range[1, 25] - 9 (* _Vincenzo Librandi_, Jan 03 2016 *)
%o A170955 (Magma) [10^n-9: n in [1..30]]; // _Vincenzo Librandi_, Feb 06 2013
%o A170955 (PARI) a(n)=10^n-9 \\ _Charles R Greathouse IV_, Oct 07 2015
%Y A170955 Cf. A093177, A193871.
%K A170955 nonn,easy
%O A170955 1,2
%A A170955 _Vincenzo Librandi_, Feb 26 2010
%E A170955 Typo in formula corrected by _Jon E. Schoenfield_, Jun 19 2010