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 A380667 #15 Jan 30 2025 15:28:10 %S A380667 0,0,-1,1,0,-1,1,0,0,0,-1,0,0,1,-1,1,0,0,-1,1,0,-1,1,-1,0,0,1,0,0,-1, %T A380667 1,0,0,0,-1,1,0,-1,1,0,0,0,-1,0,0,1,-1,0,0,0,1,-1,0,1,-1,1,0,0,-1,0,0, %U A380667 1,-1,1,0,0,-1,1,0,-1,1,0,0,0,-1,0,0,1,-1,1,0,0,-1,1,0 %N A380667 First differences of the Golay-Rudin-Shapiro sequence (A020985), divided by 2. %H A380667 Paolo Xausa, <a href="/A380667/b380667.txt">Table of n, a(n) for n = 0..10000</a> %F A380667 a(n) = (A020985(n+1) - A020985(n))/2. %t A380667 Differences[RudinShapiro[Range[0, 100]]]/2 %o A380667 (Python) %o A380667 def A380667(n): return (1 if m else -1) if (m:=(n&(n>>1)).bit_count()&1)^((n+1&(n+1>>1)).bit_count()&1) else 0 # _Chai Wah Wu_, Jan 30 2025 %Y A380667 Cf. A020985, A020986. %K A380667 sign,easy %O A380667 0,3 %A A380667 _Paolo Xausa_, Jan 30 2025