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 A173812 #22 Sep 09 2024 12:48:32
%S A173812 7,87,887,8887,88887,888887,8888887,88888887,888888887,8888888887,
%T A173812 88888888887,888888888887,8888888888887,88888888888887,
%U A173812 888888888888887,8888888888888887,88888888888888887,888888888888888887,8888888888888888887,88888888888888888887,888888888888888888887
%N A173812 a(n) = (8*10^n - 17)/9 for n > 0.
%H A173812 Vincenzo Librandi, <a href="/A173812/b173812.txt">Table of n, a(n) for n = 1..100</a>
%H A173812 <a href="/index/Rec#order_02">Index entries for linear recurrences with constant coefficients</a>, signature (11,-10).
%F A173812 a(n) = 10*a(n-1) + 17 with n > 0, a(0)=-1.
%F A173812 From _Vincenzo Librandi_, Jul 05 2012: (Start)
%F A173812 a(n) = 11*a(n-1) - 10*a(n-2) for n > 2.
%F A173812 G.f.: x*(7+10*x)/((1-x)*(1-10*x)). (End)
%F A173812 E.g.f.: 1 + exp(x)*(8*exp(9*x) - 17)/9. - _Elmo R. Oliveira_, Sep 09 2024
%t A173812 CoefficientList[Series[(7+10*x)/((1-x)*(1-10*x)),{x,0,30}],x] (* _Vincenzo Librandi_, Jul 05 2012 *)
%t A173812 Table[FromDigits[PadLeft[{7},n,8]],{n,20}] (* _Harvey P. Dale_, Jun 22 2013 *)
%o A173812 (Magma) [(8*10^n-17)/9: n in [1..20]]; // _Vincenzo Librandi_, Jul 05 2012
%Y A173812 Cf. A093171.
%K A173812 nonn,easy
%O A173812 1,1
%A A173812 _Vincenzo Librandi_, Feb 25 2010