%I #9 Apr 27 2015 10:40:15
%S 7,3,11,9,2,13,4,5,8,17,19,10,21,23,25,29,31,35,37,15,41,43,47,16,53,
%T 20,59,22,49,61,27,14,55,26,67,28,33,65,32,71,34,73,38,79,44,83,39,77,
%U 51,89,91,57,85,97,40,63,101,103,107,109,113,95,127,115,6
%N Construct spiral of numbers on square grid as in Comments; sequence gives terms along the "7" arm.
%C Place numbers 2,3,5,7 clockwise around a grid point (see illustrations in links). Divide grid into four spiral arms.
%C Extend each arm one step at a time, in rotation: first the 2 arm, then the 3 arm, then the 5 arm, then the 7 arm, then the 2 arm, etc.
%C Rule for extending: next term in arm is smallest number such that each cell in the grid is relatively prime to its eight neighbors. Inside an arm, the terms must be distinct.
%C Repetitions between arms are permitted.
%C The four arms are A257325, A257326, A257327, A257328.
%H Lars Blomberg, <a href="/A257328/b257328.txt">Table of n, a(n) for n = 1..10000</a>
%H Popular Computing (Calabasas, CA), <a href="/A257321/a257321.png">Problem 146: Gcd</a>, Vol. 4 (No. 45, Dec 1976), page PC45-4.
%H N. J. A. Sloane, <a href="/A257321/a257321_1.png">Spirals showing initial terms of A257321-A257332</a>
%Y Cf. A064413, A257321-A257340.
%K nonn
%O 1,1
%A _N. J. A. Sloane_, Apr 21 2015
%E More terms from _Lars Blomberg_, Apr 27 2015