A257323 - OEIS

%I #12 Apr 28 2015 11:01:53

%S 5,2,11,2,5,7,2,5,7,3,5,3,5,3,7,3,2,11,3,5,7,2,7,2,7,2,5,2,3,2,5,2,5,

%T 7,3,7,3,5,3,5,7,2,5,7,3,7,3,7,3,2,11,3,5,3,5,3,5,3,7,3,2,5,2,5,2,7,2,

%U 7,2,3,5,7,2,7,2,7,2,7,2,5,7,3,5,11,2,5

%N Construct spiral of numbers on square grid as in Comments; sequence gives terms along the "5" 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="/A257323/b257323.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