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 A134430 #17 Dec 12 2023 09:00:33
%S A134430 1,-2,-2,1,1,-2,-2,1,1,-2,-2,1,1,-2,-2,1,1,-2,-2,1,1,-2,-2,1,1,-2,-2,
%T A134430 1,1,-2,-2,1,1,-2,-2,1,1,-2,-2,1,1,-2,-2,1,1,-2,-2,1,1,-2,-2,1,1,-2,
%U A134430 -2,1,1,-2,-2,1,1,-2,-2,1,1,-2,-2,1,1,-2,-2,1,1,-2
%N A134430 Period 4: repeat [1, -2, -2, 1].
%H A134430 <a href="/index/Rec#order_03">Index entries for linear recurrences with constant coefficients</a>, signature (1,-1,1).
%F A134430 Binomial transform of A134813.
%F A134430 |a(n)| = A014695(n).
%F A134430 G.f.: (1-3*x+x^2) / ((1-x)*(1+x^2)). - _R. J. Mathar_, Jan 18 2011
%F A134430 From _Wesley Ivan Hurt_, Jul 09 2016: (Start)
%F A134430 a(n) = a(n-1) - a(n-2) + a(n-3) for n>2, a(n) = a(n-4) for n>3.
%F A134430 a(n) = (3*cos(n*Pi/2) - 3*sin(n*Pi/2) - 1)/2. (End)
%p A134430 seq(op([1, -2, -2, 1]), n=0..40); # _Wesley Ivan Hurt_, Jul 09 2016
%t A134430 PadRight[{}, 100, {1, -2, -2, 1}] (* _Wesley Ivan Hurt_, Jul 09 2016 *)
%o A134430 (Magma) &cat [[1, -2, -2, 1]^^30]; // _Wesley Ivan Hurt_, Jul 09 2016
%Y A134430 Cf. A014695, A134813.
%K A134430 sign,easy
%O A134430 0,2
%A A134430 _Paul Curtz_, Jan 31 2008