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 A101675 #41 Sep 08 2022 08:45:16
%S A101675 1,-1,-2,1,1,0,1,-1,-2,1,1,0,1,-1,-2,1,1,0,1,-1,-2,1,1,0,1,-1,-2,1,1,
%T A101675 0,1,-1,-2,1,1,0,1,-1,-2,1,1,0,1,-1,-2,1,1,0,1,-1,-2,1,1,0,1,-1,-2,1,
%U A101675 1,0,1,-1,-2,1,1,0,1,-1,-2,1,1,0,1,-1,-2,1,1,0,1,-1,-2,1,1,0,1,-1,-2,1,1,0,1,-1,-2,1,1,0,1,-1,-2,1,1,0,1,-1,-2
%N A101675 Expansion of (1 - x - x^2)/(1 + x^2 + x^4).
%C A101675 Partial sums are A101676.
%C A101675 Periodic with period 6. - _Ray Chandler_, Sep 03 2015
%H A101675 G. C. Greubel, <a href="/A101675/b101675.txt">Table of n, a(n) for n = 0..10000</a>
%H A101675 <a href="/index/Rec#order_04">Index entries for linear recurrences with constant coefficients</a>, signature (0,-1,0,-1).
%F A101675 a(0) = 1, a(1) = -1, a(2) = -2, a(3) = 1; for n >= 4, a(n) = -a(n-2)-a(n-4).
%F A101675 a(n) = Sum_{k=0..floor(n/2)} (-1)^A010060(n-2k)*(binomial(n-k, k) mod 2)*(-1)^k.
%F A101675 a(n) = cos(2*Pi*n/3 + Pi/6)/sqrt(3) + sin(2*Pi*n/3 + Pi/6) + cos(Pi*n/3 + Pi/3) - sin(Pi*n/3 + Pi/3)/sqrt(3).
%F A101675 a(n) = (-1)^(n+1)*H(n + 4, n mod 2, 1/2) where H(n, a, b) = hypergeom([a - n/2, b - n/2], [1 - n], 4). - _Peter Luschny_, Sep 03 2019
%t A101675 LinearRecurrence[{0, -1, 0, -1},{1, -1, -2, 1},105] (* _Ray Chandler_, Sep 03 2015 *)
%t A101675 CoefficientList[Series[(1 - x - x^2)/(1 + x^2 + x^4), {x, 0, 150}], x] (* _Vincenzo Librandi_, Sep 04 2015 *)
%o A101675 (PARI) Vec((1-x-x^2)/(1+x^2+x^4) + O(x^80)) \\ _Michel Marcus_, Sep 04 2015
%o A101675 (Magma) I:=[1,-1,-2,1]; [n le 4 select I[n] else -Self(n-2)-Self(n-4): n in [1..120]]; // _Vincenzo Librandi_, Sep 04 2015
%Y A101675 Cf. A101676.
%K A101675 easy,sign
%O A101675 0,3
%A A101675 _Paul Barry_, Dec 11 2004