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 A173768 #21 Jun 23 2025 00:06:05
%S A173768 1,41,441,4441,44441,444441,4444441,44444441,444444441,4444444441,
%T A173768 44444444441,444444444441,4444444444441,44444444444441,
%U A173768 444444444444441,4444444444444441,44444444444444441,444444444444444441,4444444444444444441,44444444444444444441,444444444444444444441
%N A173768 a(n) = (4*10^n - 31)/9.
%H A173768 Vincenzo Librandi, <a href="/A173768/b173768.txt">Table of n, a(n) for n = 1..100</a>
%H A173768 <a href="/index/Rec#order_02">Index entries for linear recurrences with constant coefficients</a>, signature (11,-10).
%F A173768 a(n) = 10*a(n-1) + 31, n>1.
%F A173768 G.f.: x*(1+30*x)/((10*x-1)*(x-1)).
%F A173768 From _Elmo R. Oliveira_, Jun 19 2025: (Start)
%F A173768 E.g.f.: 3 + exp(x)*(4*exp(9*x) - 31)/9.
%F A173768 a(n) = 11*a(n-1) - 10*a(n-2) for n > 2. (End)
%t A173768 NestList[10#+31&,1,20] (* or *) Table[FromDigits[PadLeft[{1},n,4]],{n,20}] (* _Harvey P. Dale_, May 28 2013 *)
%t A173768 Table[(4 10^n - 31)/9, {n, 1, 30}] (* _Vincenzo Librandi_, Aug 20 2014 *)
%o A173768 (Magma) [(4*10^n-31)/9: n in [1..20]]; // _Vincenzo Librandi_, Aug 20 2014
%Y A173768 Cf. A093174.
%K A173768 nonn,easy
%O A173768 1,2
%A A173768 _Vincenzo Librandi_, Feb 24 2010