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 A322925 #23 Jun 09 2025 14:31:39
%S A322925 0,1,2,21,22,221,222,2221,2222,22221,22222,222221,222222,2222221,
%T A322925 2222222,22222221,22222222,222222221,222222222,2222222221,2222222222,
%U A322925 22222222221,22222222222,222222222221,222222222222,2222222222221,2222222222222,22222222222221
%N A322925 Expansion of x*(1 + 2*x + 10*x^2)/((1 - x^2)*(1 - 10*x^2)).
%H A322925 Muniru A Asiru, <a href="/A322925/b322925.txt">Table of n, a(n) for n = 0..1000</a>
%H A322925 <a href="/index/Rec#order_04">Index entries for linear recurrences with constant coefficients</a>, signature (0,11,0,-10).
%F A322925 G.f.: x*(1 + 2*x + 10*x^2)/((1 - x^2)*(1 - 10*x^2)).
%F A322925 a(n) = 11*a(n-2) - 10* a(n-4).
%F A322925 a(n) = 2*(10^n - 1)/9 for n even; a(n) = (2*10^n - 11)/9 otherwise.
%F A322925 a(n) = (2/9)*10^floor((n + 1)/2) + (-1)^n/2 - 13/18. - _Bruno Berselli_, Mar 16 2019
%p A322925 seq(coeff(series(x*(1+2*x+10*x^2)/((1-x^2)*(1-10*x^2)),x,n+1), x, n), n = 0 .. 30); # _Muniru A Asiru_, Apr 10 2019
%t A322925 CoefficientList[Series[x (1 + 2 x + 10 x^2)/((1 - x^2) (1 - 10 x^2)), {x, 0, 33}], x]
%t A322925 LinearRecurrence[{0,11,0,-10},{0,1,2,21},30] (* _Harvey P. Dale_, Mar 02 2021 *)
%o A322925 (Magma) I:=[0,1,2,21]; [n le 4 select I[n] else 11*Self(n-2)-10*Self(n-4): n in [1..30]];
%o A322925 (GAP) a:=[0,1,2,21];; for n in [5..30] do a[n]:=11*a[n-2]-10*a[n-4]; od; Print(a); # _Muniru A Asiru_, Apr 10 2019
%Y A322925 Bisections give: A002276 (even part), A165402 (odd part).
%K A322925 nonn,easy
%O A322925 0,3
%A A322925 _Vincenzo Librandi_, Mar 16 2019