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 A101676 #24 Dec 14 2023 05:16:09
%S A101676 1,0,-2,-1,0,0,1,0,-2,-1,0,0,1,0,-2,-1,0,0,1,0,-2,-1,0,0,1,0,-2,-1,0,
%T A101676 0,1,0,-2,-1,0,0,1,0,-2,-1,0,0,1,0,-2,-1,0,0,1,0,-2,-1,0,0,1,0,-2,-1,
%U A101676 0,0,1,0,-2,-1,0,0,1,0,-2,-1,0,0,1,0,-2,-1,0,0,1,0,-2,-1,0,0,1,0,-2,-1,0,0,1,0,-2,-1,0,0,1,0,-2,-1,0,0,1,0,-2
%N A101676 a(n) = a(n-1) - a(n-2) + a(n-3) - a(n-4) + a(n-5) with initial terms 1,0,-2,-1,0.
%C A101676 Partial sums of A101675. Partial sums are A101677.
%C A101676 Sequence has period 6. - _Ralf Stephan_, May 16 2007
%H A101676 G. C. Greubel, <a href="/A101676/b101676.txt">Table of n, a(n) for n = 0..10000</a>
%H A101676 <a href="/index/Rec#order_05">Index entries for linear recurrences with constant coefficients</a>, signature (1,-1,1,-1,1).
%F A101676 G.f.: (1 - x - x^2)/((1 - x)*(1 + x^2 + x^4)).
%F A101676 a(n) = -cos(2*Pi*n/3+Pi/3)/3 + sin(2*Pi*n/3+Pi/3)/sqrt(3) + 2*cos(Pi*n/3+Pi/6)/sqrt(3) - 1/3.
%t A101676 LinearRecurrence[{1, -1, 1, -1, 1},{1, 0, -2, -1, 0},105] (* _Ray Chandler_, Sep 03 2015 *)
%o A101676 (PARI) x='x+O('x^100); Vec((1-x-x^2)/((1-x)*(1+x^2+x^4))) \\ _G. C. Greubel_, Sep 07 2018
%o A101676 (Magma) I:=[1, 0, -2, -1, 0]; [n le 5 select I[n] else Self(n-1) - Self(n-2) +Self(n-3) -Self(n-4) +Self(n-5): n in [1..100]]; // _G. C. Greubel_, Sep 07 2018
%K A101676 sign,easy
%O A101676 0,3
%A A101676 _Paul Barry_, Dec 11 2004