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 A122434 #17 May 10 2024 10:58:48
%S A122434 1,2,0,-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,
%T A122434 -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,
%U A122434 0,-1,1,0,-1,1,0,-1,1,0
%N A122434 Expansion of (1+x)^3/(1+x+x^2).
%C A122434 Row sums of number triangle A122433. Binomial transform is A077859.
%H A122434 <a href="/index/Rec#order_02">Index entries for linear recurrences with constant coefficients</a>, signature (-1,-1).
%F A122434 a(n) = 2*sqrt(3)*cos(2*Pi*n/3+Pi/6)/3+C(1,n)+C(0,n).
%F A122434 a(n) = -A049347(n) if n>=2 . - _R. J. Mathar_, Feb 08 2008
%t A122434 CoefficientList[Series[(1+x)^3/(1+x+x^2),{x,0,70}],x] (* or *) PadRight[ {1,2,0},71,{-1,1,0}] (* _Harvey P. Dale_, Apr 25 2012 *)
%K A122434 easy,sign
%O A122434 0,2
%A A122434 _Paul Barry_, Sep 04 2006