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 A304580 #21 Nov 19 2023 21:16:25
%S A304580 1,8,3,6,5,4,7,2,9,0,7,2,5,4,3,6,1,8,3,6,5,4,7,2,9,0,7,2,5,4,3,6,1,8,
%T A304580 3,6,5,4,7,2,9,0,7,2,5,4,3,6,1,8,3,6,5,4,7,2,9,0,7,2,5,4,3,6,1,8,3,6,
%U A304580 5,4,7,2,9,0,7,2,5,4,3,6,1,8,3,6,5,4
%N A304580 Period 16: repeat 1,8,3,6,5,4,7,2,9,0,7,2,5,4,3,6.
%C A304580 Repeating sequences of alternating odd and even single digits that in pairs sum to 9, 11 or 7. Note that 1836547290725436 = 20202020197979796 / 11.
%H A304580 Colin Barker, <a href="/A304580/b304580.txt">Table of n, a(n) for n = 1..1000</a>
%H A304580 <a href="/index/Rec#order_10">Index entries for linear recurrences with constant coefficients</a>, signature (0,1,0,0,0,0,0,-1,0,1).
%F A304580 From _Colin Barker_, May 28 2018: (Start)
%F A304580 G.f.: x*(1 + 8*x + 2*x^2 - 2*x^3 + 2*x^4 - 2*x^5 + 2*x^6 - 2*x^7 + 3*x^8 + 6*x^9) / ((1 - x)*(1 + x)*(1 + x^8)).
%F A304580 a(n) = a(n-2) - a(n-8) + a(n-10) for n > 10.
%F A304580 (End)
%t A304580 LinearRecurrence[{0,1,0,0,0,0,0,-1,0,1},{1,8,3,6,5,4,7,2,9,0},100] (* or *) PadRight[{},100,{1,8,3,6,5,4,7,2,9,0,7,2,5,4,3,6}] (* _Harvey P. Dale_, Sep 28 2021 *)
%o A304580 (PARI) Vec(x*(1 + 8*x + 2*x^2 - 2*x^3 + 2*x^4 - 2*x^5 + 2*x^6 - 2*x^7 + 3*x^8 + 6*x^9) / ((1 - x)*(1 + x)*(1 + x^8)) + O(x^50)) \\ _Colin Barker_, May 28 2018
%Y A304580 Cf. A172423, A172430, A304583.
%K A304580 nonn,easy
%O A304580 1,2
%A A304580 _Halfdan Skjerning_, May 15 2018