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%I #11 Apr 30 2015 20:04:51
%S 7,9,23,15,14,47,12,59,22,65,83,26,97,101,103,119,81,137,133,143,149,
%T 93,161,48,179,42,191,54,199,129,217,66,233,56,247,82,257,271,88,283,
%U 92,183,98,305,104,319,325,329,335,231,353,355,373,377,118,383,401
%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. Every term in the entire grid must be different.
%C The four arms are A257329, A257330, A257331, A257332.
%C Conjecture: every number > 1 appears in one of the four arms.
%H Lars Blomberg, <a href="/A257332/b257332.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, A257347 (the union list).
%K nonn
%O 1,1
%A _N. J. A. Sloane_, Apr 21 2015
%E More terms from _Lars Blomberg_, Apr 27 2015
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