%N Consider the numbers on the x-axis in the spiral shown in A274641; a(n) is the distance from n to the origin, or -1 if n never appears on the x-axis.
%C It is conjectured that every nonnegative number appears on the x-axis exactly once.
%C a(n) is also the distance to the origin from the point n+1 on the x-axis in A274640.
%C Needs a large b-file: it will be interesting to see how irregular this sequence is.
%e The portion of the x-axis near 0 is:
%e ... 14 6 5 4 2 0 1 3 7 10 11 ...
%e and we see that both 1 and 2 are at distance 1 from 0. So a(1) = a(2) = 1.
%Y Cf. A274640, A274641.
%Y The positive and negative x-axes are given in A274924 and A274928.
%A _N. J. A. Sloane_, Mar 11 2019