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 A211023 #31 Jan 16 2023 08:16:46
%S A211023 0,-1,-3,-5,-5,-3,-3,-5,-5,-3,-1,1,1,-1,-1,1,3,5,7,7,5,3,3,5,5,5,7,7,
%T A211023 5,5,7,7,5,3,1,-1,-3,-5,-5,-3,-1,1,3,5,5,3,3,3,3,5,5,3,1,-1,-3,-5,-7,
%U A211023 -9,-11,-11,-9,-7,-5,-5,-7,-7,-5,-3,-1,1,1,-1,-1,1,3
%N A211023 Value on the axis "y" of the endpoint of the structure of A211000 if the index is prime.
%C A211023 a(n) is also the value on the axis "y" of the n-th inflection point in the structure of A211000.
%C A211023 The behavior seems to be as modular arithmetic but in a growing structure. The structure of A211000 looks like essentially a column of tangent circles of radius 1. The structure of A211000 arises from the prime numbers A000040.
%H A211023 Paolo Xausa, <a href="/A211023/b211023.txt">Table of n, a(n) for n = 1..10000</a>
%F A211023 a(n) = A211011(A000040(n)).
%t A211023 A211023[upto_]:=Module[{ep={0, 0}, angle=3/4Pi, turn=Pi/2}, Table[If[!PrimeQ[n], If[n>5&&PrimeQ[n-1], turn*=-1]; angle-=turn]; ep=AngleVector[ep, {Sqrt[2], angle}];If[PrimeQ[n+1], Last[ep], Nothing], {n, 0,upto-1}]];
%t A211023 A211023[500] (* _Paolo Xausa_, Jan 14 2023 *)
%Y A211023 Cf. A187210, A211000, A211001, A211002, A211003, A211010, A211011, A211020, A211021, A211022, A211024.
%K A211023 sign
%O A211023 1,3
%A A211023 _Omar E. Pol_, Mar 31 2012