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 A002278 #50 Jul 20 2025 08:56:33
%S A002278 0,4,44,444,4444,44444,444444,4444444,44444444,444444444,4444444444,
%T A002278 44444444444,444444444444,4444444444444,44444444444444,
%U A002278 444444444444444,4444444444444444,44444444444444444,444444444444444444,4444444444444444444,44444444444444444444,444444444444444444444
%N A002278 a(n) = 4*(10^n - 1)/9.
%H A002278 Ivan Panchenko, <a href="/A002278/b002278.txt">Table of n, a(n) for n = 0..200</a>
%H A002278 <a href="/index/Rec#order_02">Index entries for linear recurrences with constant coefficients</a>, signature (11,-10).
%F A002278 a(n) = A075415(n)/A002283(n). - _Reinhard Zumkeller_, May 31 2010
%F A002278 From _Vincenzo Librandi_, Jul 22 2010: (Start)
%F A002278 a(n) = a(n-1) + 4*10^(n-1) with a(0)=0;
%F A002278 a(n) = 11*a(n-1) - 10*a(n-2) with a(0)=0, a(1)=4. (End)
%F A002278 G.f.: 4*x/((1 - x)*(1 - 10*x)). - _Ilya Gutkovskiy_, Feb 24 2017
%F A002278 E.g.f.: 4*exp(x)*(exp(9*x) - 1)/9. - _Stefano Spezia_, Sep 13 2023
%F A002278 a(n) = A007091(A024049(n)). - _Michel Marcus_, Jun 16 2024
%F A002278 From _Elmo R. Oliveira_, Jul 19 2025: (Start)
%F A002278 a(n) = 4*A002275(n).
%F A002278 a(n) = A010785(A017209(n-1)) for n >= 1. (End)
%t A002278 LinearRecurrence[{11, -10}, {0, 4}, 20] (* _Robert G. Wilson v_, Jul 06 2013 *)
%o A002278 (PARI) a(n)=4*(10^n-1)/9 \\ _Charles R Greathouse IV_, Sep 24 2015
%Y A002278 Cf. A002275, A002276, A002277, A002279, A002280, A002281, A002282, A002283, A075415, A178632.
%Y A002278 Cf. A007091, A010785, A017209, A024049.
%K A002278 easy,nonn
%O A002278 0,2
%A A002278 _N. J. A. Sloane_