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 A173807 #20 Sep 09 2024 12:49:40
%S A173807 3,73,773,7773,77773,777773,7777773,77777773,777777773,7777777773,
%T A173807 77777777773,777777777773,7777777777773,77777777777773,
%U A173807 777777777777773,7777777777777773,77777777777777773,777777777777777773,7777777777777777773,77777777777777777773,777777777777777777773
%N A173807 a(n) = (7*10^n - 43)/9 for n > 0.
%H A173807 Vincenzo Librandi, <a href="/A173807/b173807.txt">Table of n, a(n) for n = 1..100</a>
%H A173807 <a href="/index/Rec#order_02">Index entries for linear recurrences with constant coefficients</a>, signature (11,-10).
%F A173807 a(n) = 10*a(n-1) + 43 for n > 0, a(0)=-4.
%F A173807 From _Vincenzo Librandi_, Jul 05 2012: (Start)
%F A173807 G.f.: x*(3+40*x)/((1-x)*(1-10*x)).
%F A173807 a(n) = 11*a(n-1) - 10*a(n-2) for n > 2. (End)
%F A173807 E.g.f.: 4 + exp(x)*(7*exp(9*x) - 43)/9. - _Elmo R. Oliveira_, Sep 09 2024
%t A173807 CoefficientList[Series[(3+40*x)/((1-x)*(1-10*x)),{x,0,30}],x] (* _Vincenzo Librandi_, Jul 05 2012 *)
%t A173807 Table[FromDigits[PadLeft[{3},n,7]],{n,20}] (* or *) NestList[10#+43&,3,20] (* _Harvey P. Dale_, Dec 05 2013 *)
%o A173807 (Magma)[(7*10^n-43)/9: n in [1..20]]; // _Vincenzo Librandi_, Jul 05 2012
%Y A173807 Cf. A093165.
%K A173807 nonn,easy
%O A173807 1,1
%A A173807 _Vincenzo Librandi_, Feb 25 2010