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 A198973 #19 Jun 12 2025 00:47:33
%S A198973 7,79,799,7999,79999,799999,7999999,79999999,799999999,7999999999,
%T A198973 79999999999,799999999999,7999999999999,79999999999999,
%U A198973 799999999999999,7999999999999999,79999999999999999,799999999999999999,7999999999999999999,79999999999999999999,799999999999999999999
%N A198973 a(n) = 8*10^n - 1.
%H A198973 Vincenzo Librandi, <a href="/A198973/b198973.txt">Table of n, a(n) for n = 0..200</a>
%H A198973 <a href="/index/Rec#order_02">Index entries for linear recurrences with constant coefficients</a>, signature (11,-10).
%F A198973 a(n) = 10*a(n-1) + 9.
%F A198973 a(n) = 11*a(n-1) - 10*a(n-2), n>1.
%F A198973 G.f.: (7 + 2*x)/(1 - 11*x + 10*x^2). - _Vincenzo Librandi_, Jan 04 2013
%F A198973 E.g.f.: exp(x)*(8*exp(9*x) - 1). - _Elmo R. Oliveira_, Jun 10 2025
%t A198973 Table[FromDigits[PadRight[{7},n,9]],{n,20}] (* _Harvey P. Dale_, Jun 05 2012 *)
%t A198973 CoefficientList[Series[(7 + 2*x)/(1 - 11*x + 10*x^2), {x, 0, 30}], x] (* _Vincenzo Librandi_, Jan 04 2013 *)
%o A198973 (Magma) [8*10^n-1 : n in [0..20]];
%K A198973 nonn,easy
%O A198973 0,1
%A A198973 _Vincenzo Librandi_, Nov 02 2011