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 A304583 #28 Feb 10 2024 17:31:32
%S A304583 1,8,3,6,5,4,7,2,9,0,9,2,7,4,5,6,3,8,1,8,3,6,5,4,7,2,9,0,9,2,7,4,5,6,
%T A304583 3,8,1,8,3,6,5,4,7,2,9,0,9,2,7,4,5,6,3,8,1,8,3,6,5,4,7,2,9,0,9,2,7,4,
%U A304583 5,6,3,8,1,8,3,6,5,4,7,2,9,0,9,2,7,4
%N A304583 Period 18: repeat 1,8,3,6,5,4,7,2,9,0,9,2,7,4,5,6,3,8.
%C A304583 Repeating sequences of alternating odd and even single digits that in pairs sum to 9 or 11. Note that 183654729092745638 = 2020202020020202018 / 11.
%H A304583 Colin Barker, <a href="/A304583/b304583.txt">Table of n, a(n) for n = 1..1000</a>
%H A304583 <a href="/index/Rec#order_10">Index entries for linear recurrences with constant coefficients</a>, signature (-1,0,0,0,0,0,0,0,1,1).
%F A304583 From _Colin Barker_, May 28 2018: (Start)
%F A304583 G.f.: x*(1 + 9*x + 11*x^2 + 9*x^3 + 11*x^4 + 9*x^5 + 11*x^6 + 9*x^7 + 11*x^8 + 8*x^9) / ((1 - x)*(1 + x)*(1 + x + x^2)*(1 + x^3 + x^6)).
%F A304583 a(n) = -a(n-1) + a(n-9) + a(n-10) for n > 10.
%F A304583 (End)
%t A304583 PadRight[{},120,{1,8,3,6,5,4,7,2,9,0,9,2,7,4,5,6,3,8}] (* _Harvey P. Dale_, Feb 10 2024 *)
%o A304583 (PARI) Vec(x*(1 + 9*x + 11*x^2 + 9*x^3 + 11*x^4 + 9*x^5 + 11*x^6 + 9*x^7 + 11*x^8 + 8*x^9) / ((1 - x)*(1 + x)*(1 + x + x^2)*(1 + x^3 + x^6)) + O(x^50)) \\ _Colin Barker_, May 28 2018
%Y A304583 Cf. A172423, A172430, A304580.
%K A304583 nonn,easy
%O A304583 1,2
%A A304583 _Halfdan Skjerning_, May 15 2018