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%I #27 Apr 27 2015 10:36:58
%S 2,5,7,5,3,11,5,2,7,2,3,2,5,2,5,7,3,5,7,2,5,7,11,3,7,3,5,3,5,3,5,3,7,
%T 3,2,5,2,7,2,3,5,7,2,7,2,7,2,7,2,5,11,2,5,2,3,2,5,2,5,7,3,7,3,7,3,5,3,
%U 5,3,5,7,2,5,7,3,7,3,7,3,2,5,2,7,2,3,5
%N Construct spiral of numbers on square grid as in Comments; sequence gives terms along the "2" 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.
%C Repetitions in arms are permitted.
%C The four arms are A257321, A257322, A257323, A257324.
%H Lars Blomberg, <a href="/A257321/b257321.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, A257322-A257340.
%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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