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 A089809 #15 Aug 17 2022 22:20:39
%S A089809 0,1,0,1,1,0,1,0,0,1,0,1,1,0,1,0,0,1,0,1,0,0,1,0,1,1,0,1,0,0,1,0,1,1,
%T A089809 0,1,0,1,1,0,1,0,0,1,0,1,1,0,1,0,0,1,0,1,0,0,1,0,1,1
%N A089809 Complement of A078588.
%C A089809 a(n) = 1 if (fractional part of n*r) < 1/2, else a(n) = 0, where r = golden ratio = (1 + sqrt(5))/2. - _Clark Kimberling_, Dec 27 2016
%H A089809 Clark Kimberling, <a href="/A089809/b089809.txt">Table of n, a(n) for n = 1..10000</a>
%F A089809 a(n) = 1 if A078588 = 0; otherwise, not.
%F A089809 a(n) = 1 iff A024569 is not 1.
%F A089809 a(n) = 1 iff A089808 is 1.
%F A089809 a(n) = 1 if (fractional part of n*r) < 1/2, else a(n) = 0. - _Clark Kimberling_, Dec 27 2016
%e A089809 1. a(7) = 1 since A078588(7) = 0
%e A089809 2. a(7) = 1 since A024569 is not 1 (A024569(7) = 3).
%e A089809 3. a(7) = 1 since A089808(7) = 1.
%t A089809 r = GoldenRatio; z = 500;
%t A089809 Table[If[FractionalPart[n r] < 1/2, 1, 0 ], {n, 1, z}] (* A089809 *)
%t A089809 Table[If[FractionalPart[n r] > 1/2, 1, 0 ], {n, 1, z}] (* A078588 *)
%t A089809 1 - % (* A089809, _Clark Kimberling_, Dec 27 2016 *)
%o A089809 (Python)
%o A089809 from math import isqrt
%o A089809 def A089809(n): return ((n+isqrt(5*n**2))&1)^1 # _Chai Wah Wu_, Aug 17 2022
%Y A089809 Cf. A078588, A024569, A089808.
%K A089809 nonn
%O A089809 1,1
%A A089809 _Gary W. Adamson_, Nov 11 2003