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 A033146 #42 Jan 02 2025 02:55:23
%S A033146 1,10,100,1001,10010,100100,1001001,10010010,100100100,1001001001,
%T A033146 10010010010,100100100100,1001001001001,10010010010010,
%U A033146 100100100100100,1001001001001001,10010010010010010,100100100100100100,1001001001001001001,10010010010010010010
%N A033146 Decimal expansion of a(n) is given by the first n terms of the periodic sequence with initial period 1,0,0.
%H A033146 <a href="/index/Rec#order_04">Index entries for linear recurrences with constant coefficients</a>, signature (10,0,1,-10).
%F A033146 From _Paul Barry_, Apr 16 2005: (Start)
%F A033146 G.f.: 1/((1-x^3)*(1-10*x)).
%F A033146 a(n) = 10*a(n-1) + a(n-3) - 10*a(n-4).
%F A033146 a(n) = Sum_{k=0..floor(n/3)} 10^(n-3k), with offset 0.
%F A033146 a(n) = Sum_{k=0..n} 10^k*(cos(2*Pi*(n-k)/3 + Pi/3)/3 + sqrt(3)*sin(2*Pi*(n-k)/3 + Pi/3)/3 + 1/3), with offset 0. (End)
%F A033146 a(n) = round( (100/999)*10^n ). - _Tani Akinari_, Jul 15 2014
%t A033146 With[{c = PadLeft[{}, 21, {1, 0, 0}]}, Table[FromDigits[Take[c, n]], {n, 20}]] (* _Harvey P. Dale_, Oct 03 2011 *)
%o A033146 (Python) print([100*10**n//999 for n in range(1,50)]) # _Karl V. Keller, Jr._, Oct 05 2021
%K A033146 nonn,base,easy
%O A033146 1,2
%A A033146 _Clark Kimberling_