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 A322927 #18 Sep 08 2022 08:46:23
%S A322927 0,1,5,51,55,551,555,5551,5555,55551,55555,555551,555555,5555551,
%T A322927 5555555,55555551,55555555,555555551,555555555,5555555551,5555555555,
%U A322927 55555555551,55555555555,555555555551,555555555555,5555555555551,5555555555555,55555555555551
%N A322927 Expansion of x*(1 + 5*x + 40*x^2)/((1 - x^2)*(1 - 10*x^2)).
%H A322927 Muniru A Asiru, <a href="/A322927/b322927.txt">Table of n, a(n) for n = 0..1000</a>
%H A322927 <a href="/index/Rec#order_04">Index entries for linear recurrences with constant coefficients</a>, signature (0,11,0,-10).
%F A322927 G.f.: x*(1 + 5*x + 40*x^2)/((1 - x^2)*(1 - 10*x^2)).
%F A322927 a(n) = 11*a(n-2) - 10*a(n-4).
%F A322927 a(n) = 5*(10^n - 1)/9 for n even; a(n) = (5*10^n - 41)/9 otherwise.
%p A322927 seq(coeff(series(x*(1+5*x+40*x^2)/((1-x^2)*(1-10*x^2)),x,n+1), x, n), n = 0 .. 30); # _Muniru A Asiru_, Mar 17 2019
%t A322927 CoefficientList[Series[x (1 + 5 x + 40 x^2) / (10 x^4 - 11 x^2 + 1), {x, 0, 25}], x]
%o A322927 (Magma) I:=[0, 1, 5, 51]; [n le 4 select I[n] else 11*Self(n-2)-10*Self(n-4): n in [1..30]];
%Y A322927 Bisections give: A002279 (even part), A173804 (odd part).
%K A322927 nonn,easy
%O A322927 0,3
%A A322927 _Vincenzo Librandi_, Mar 17 2019