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 A174784 #19 Dec 12 2023 07:39:49
%S A174784 0,1,-1,0,1,1,0,-1,1,0,-1,-1,0,1,-1,0,1,1,0,-1,1,0,-1,-1,0,1,-1,0,1,1,
%T A174784 0,-1,1,0,-1,-1,0,1,-1,0,1,1,0,-1,1,0,-1,-1,0,1,-1,0,1,1,0,-1,1,0,-1,
%U A174784 -1,0,1,-1,0,1,1,0,-1,1,0,-1,-1,0,1,-1,0,1,1,0,-1,1,0,-1,-1,0,1,-1,0,1,1,0
%N A174784 Expansion of x*(1-x+x^3+x^4)/(1+x^6) (Period 12).
%C A174784 Hankel transform of A174783 is -a(n).
%H A174784 <a href="/index/Rec#order_06">Index entries for linear recurrences with constant coefficients</a>, signature (0,0,0,0,0,-1).
%F A174784 a(n) = -cos(5*Pi*n/6)/3 + sin(5*Pi*n/6)/3 - cos(Pi*n/6)/3 + sin(Pi*n/6)/3 + 2*cos(Pi*n/2)/3 + 2*sin(Pi*n/2)/3.
%F A174784 G.f.: x*(1-x+x^3+x^4) / ( (1+x^2)*(x^4-x^2+1) ). - _R. J. Mathar_, Feb 10 2015
%t A174784 LinearRecurrence[{0,0,0,0,0,-1},{0,1,-1,0,1,1},100] (* or *) PadRight[ {},120,{0,1,-1,0,1,1,0,-1,1,0,-1,-1}] (* _Harvey P. Dale_, Feb 25 2017 *)
%K A174784 easy,sign
%O A174784 0,1
%A A174784 _Paul Barry_, Mar 29 2010