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 A177002 #27 Sep 08 2022 08:45:53
%S A177002 1,2,4,2,1,2,4,2,1,2,4,2,1,2,4,2,1,2,4,2,1,2,4,2,1,2,4,2,1,2,4,2,1,2,
%T A177002 4,2,1,2,4,2,1,2,4,2,1,2,4,2,1,2,4,2,1,2,4,2,1,2,4,2,1,2,4,2,1,2,4,2,
%U A177002 1,2,4,2,1,2,4,2,1,2,4,2,1,2,4,2,1,2
%N A177002 Period 4: repeat [1, 2, 4, 2].
%C A177002 Also the decimal expansion of 138/1111 and the continued fractions of (5+3*sqrt(10))/10 or (6*sqrt(10)-10)/13. - _R. J. Mathar_, Dec 13 2010
%H A177002 <a href="/index/Rec#order_04">Index entries for linear recurrences with constant coefficients</a>, signature (0,0,0,1).
%F A177002 a(n) = | A174882(n+1) / A174882(n) |.
%F A177002 G.f.: (1+2*x+4*x^2+2*x^3)/((1-x)*(1+x)*(x^2+1)). - _R. J. Mathar_, Dec 13 2010
%F A177002 a(n) = 2+(1+(-1)^n)*(1-3*I^n)/4. - _Bruno Berselli_, Mar 15 2011
%F A177002 a(n) = a(n-1) * a(n-3) / a(n-2) for n>2. - _Bruno Berselli_, Feb 04 2013
%F A177002 From _Wesley Ivan Hurt_, Jul 09 2016: (Start)
%F A177002 a(n) = a(n-4) for n>3.
%F A177002 a(n) = (9 + cos(n*Pi) - 6*cos(n*Pi/2))/4. (End)
%p A177002 seq(op([1, 2, 4, 2]), n=0..50); # _Wesley Ivan Hurt_, Jul 09 2016
%t A177002 PadRight[{}, 100, {1, 2, 4, 2}] (* _Wesley Ivan Hurt_, Jul 09 2016 *)
%o A177002 (Magma) &cat [[1, 2, 4, 2]^^30]; // _Wesley Ivan Hurt_, Jul 09 2016
%Y A177002 Cf. A174882.
%K A177002 nonn,easy
%O A177002 0,2
%A A177002 _Paul Curtz_, Dec 08 2010