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 A135695 #18 Dec 12 2023 08:43:46
%S A135695 -1,-1,-2,-2,3,3,-1,-1,-2,-2,3,3,-1,-1,-2,-2,3,3,-1,-1,-2,-2,3,3,-1,
%T A135695 -1,-2,-2,3,3,-1,-1,-2,-2,3,3,-1,-1,-2,-2,3,3,-1,-1,-2,-2,3,3,-1,-1,
%U A135695 -2,-2,3,3,-1,-1,-2,-2,3,3,-1,-1,-2,-2,3,3,-1,-1,-2,-2,3,3,-1,-1,-2,-2,3,3,-1
%N A135695 Period 6: repeat [-1, -1, -2, -2, 3, 3].
%H A135695 <a href="/index/Rec#order_04">Index entries for linear recurrences with constant coefficients</a>, signature (0,-1,0,-1).
%F A135695 From _R. J. Mathar_, Mar 31 2008: (Start)
%F A135695 a(n) = a(n-6) for n>5. a(n) = -a(n-2) - a(n-4) for n>3.
%F A135695 G.f.: -(x+1)*(3*x^2+1)/((x^2-x+1)*(x^2+x+1)). (End)
%F A135695 a(n) = (3*cos(n*Pi/3) - 9*cos(2*n*Pi/3) - 9*sqrt(3)*sin(n*Pi/3) + sqrt(3)*sin(2*n*Pi/3))/6. - _Wesley Ivan Hurt_, Jun 22 2016
%p A135695 A135695 := proc(n) op((n mod 6)+1,[ -1,-1,-2,-2,3,3]) ; end: seq(A135695(n),n=0..150) ; # _R. J. Mathar_, Feb 07 2009
%t A135695 PadRight[{}, 100, {-1, -1, -2, -2, 3, 3}] (* _Wesley Ivan Hurt_, Jun 22 2016 *)
%o A135695 (Magma) &cat [[-1, -1, -2, -2, 3, 3]^^20]; // _Wesley Ivan Hurt_, Jun 22 2016
%Y A135695 Cf. A105899.
%K A135695 sign,easy
%O A135695 0,3
%A A135695 _Paul Curtz_, Feb 24 2008
%E A135695 More periods from _R. J. Mathar_, Feb 07 2009