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 A180594 #21 Mar 12 2024 14:18:02
%S A180594 0,4,8,3,7,2,6,1,5,9,4,8,3,7,2,6,1,5,9,4,8,3,7,2,6,1,5,9,4,8,3,7,2,6,
%T A180594 1,5,9,4,8,3,7,2,6,1,5,9,4,8,3,7,2,6,1,5,9,4,8,3,7,2,6,1,5,9,4,8,3,7,
%U A180594 2,6,1,5,9,4,8,3,7,2,6,1,5,9,4,8,3,7,2,6,1,5,9,4,8,3,7,2,6,1,5,9,4,8,3,7,2
%N A180594 Digital root of 4n.
%C A180594 Period of 9. - _Robert G. Wilson v_, Sep 20 2010
%H A180594 <a href="/index/Rec#order_09">Index entries for linear recurrences with constant coefficients</a>, signature (0,0,0,0,0,0,0,0,1).
%F A180594 G.f.: -x*(9*x^8+5*x^7+x^6+6*x^5+2*x^4+7*x^3+3*x^2+8*x+4)/((x-1)*(x^2+x+1)*(x^6+x^3+1)). - _Colin Barker_, Sep 23 2012
%t A180594 f[n_] := Mod[4 n - 1, 9] + 1; f[0] = 0; Array[f, 105, 0] (* _Robert G. Wilson v_, Sep 20 2010 *)
%t A180594 Join[{0}, ReplaceAll[Table[Mod[4n, 9], {n, 99}], {0 -> 9}]] (* _Alonso del Arte_, Sep 23 2012 *)
%t A180594 LinearRecurrence[{0,0,0,0,0,0,0,0,1},{0,4,8,3,7,2,6,1,5,9},120] (* or *) PadRight[ {0},120,{9,4,8,3,7,2,6,1,5}] (* _Harvey P. Dale_, Aug 09 2022 *)
%Y A180594 Cf. A007953, A010888, A180592.
%Y A180594 Cf. A180592, A180593, A180595, A180596, A180597, A180598, A180599.
%K A180594 easy,nonn,base
%O A180594 0,2
%A A180594 _Odimar Fabeny_, Sep 10 2010
%E A180594 More terms from _Robert G. Wilson v_, Sep 20 2010