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 A307017 #15 Mar 26 2019 16:13:57 %S A307017 0,1,1,0,-1,-1,0,2,1,-1,-2,-1,1,2,2,0,-2,-2,0,3,3,2,1,-1,-2,-3,-3,-2, %T A307017 -1,1,2,3,3,0,-3,-3,0,4,2,-2,-4,-2,2,4,4,3,1,-1,-3,-4,-4,-3,-1,1,3,4, %U A307017 4,0,-4,-4,0,5,5,3,2,-2,-3,-5,-5,-3,-2,2,3,5,5,4,1 %N A307017 List coordinates (x,y) of the points in an hexagonal grid, sorted first by radial coordinate r and in case of ties, by polar angle 0 <= phi < 2*Pi in a polar coordinate system. Sequence gives the third coordinate in a barycentric coordinate system. %C A307017 Cartesian coordinates (x,y) of the grid points are converted to barycentric coordinates (i,j,k) by i = x - y/sqrt(3), j = 2*y/sqrt(3), k = x + y/sqrt(3). The sequence gives k. i is given in A307014, j is given in A307016. %H A307017 Hugo Pfoertner, <a href="/A307017/b307017.txt">Table of n, a(n) for n = 0..9060</a>, covering range r <= 50. %Y A307017 Cf. A004016, A035019, A038590, A307014, A307016. %K A307017 sign,look %O A307017 0,8 %A A307017 _Hugo Pfoertner_, Mar 21 2019