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 A010675 #31 Jul 08 2025 01:44:13
%S A010675 0,4,0,4,0,4,0,4,0,4,0,4,0,4,0,4,0,4,0,4,0,4,0,4,0,4,0,4,0,4,0,4,0,4,
%T A010675 0,4,0,4,0,4,0,4,0,4,0,4,0,4,0,4,0,4,0,4,0,4,0,4,0,4,0,4,0,4,0,4,0,4,
%U A010675 0,4,0,4,0,4,0,4,0,4,0,4,0
%N A010675 Period 2: repeat (0,4).
%H A010675 <a href="/index/Rec#order_02">Index entries for linear recurrences with constant coefficients</a>, signature (0,1).
%F A010675 a(n) = 2*(1-(-1)^n); a(n) = 4*(n mod 2) - _Paolo P. Lava_, Oct 20 2006
%F A010675 O.g.f.: -2/(1+x)-2/(x-1). - _R. J. Mathar_, Feb 19 2008
%F A010675 a(n) = 4*(1+floor((n+1)/2)-ceiling((n+1)/2)). - _Wesley Ivan Hurt_, May 21 2013
%F A010675 a(n) = 4*cos( Pi*(n+1)/2 )^2. - _Wesley Ivan Hurt_, May 21 2013
%t A010675 PadRight[{},120,{0,4}] (* _Harvey P. Dale_, Feb 11 2025 *)
%o A010675 (Magma) &cat [[0,4]^^50]; // _Bruno Berselli_, Dec 10 2015
%o A010675 (PARI) a(n)=n%2*4 \\ _Charles R Greathouse IV_, Jul 23 2016
%K A010675 nonn,easy
%O A010675 0,2
%A A010675 _N. J. A. Sloane_