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%I #41 Apr 29 2015 16:06:55
%S 1,2,3,5,4,7,6,11,9,13,17,19,8,23,29,21,25,31,37,41,35,43,47,10,49,12,
%T 53,14,15,59,27,55,39,16,61,22,51,67,18,65,24,71,26,33,32,57,73,79,83,
%U 77,85,89,97,101,28,95,34,91,38,103,107,45,109,113,20,121
%N Arrange numbers in a single clockwise spiral so that each number is relatively prime to its eight neighbors.
%C Start with 1; always choose smallest number which has not yet appeared.
%C It is conjectured that every number appears.
%H Jon E. Schoenfield and Reinhard Zumkeller, <a href="/A257339/b257339.txt">Table of n, a(n) for n = 1..100000</a> (First 10000 terms from Jon E. Schoenfield)
%H Jon E. Schoenfield, <a href="/A257339/a257339_1.png">Illustration of initial terms</a>
%H Jon E. Schoenfield, <a href="/A257339/a257339_2.png">Graph of first 18000 terms</a>
%Y Cf. A064413, A257321-A257340.
%Y Cf. A257111 (first differences), A257455 (putative inverse).
%Y Indices of primes and prime powers: A257457 and A257458.
%K nonn
%O 1,2
%A _N. J. A. Sloane_, Apr 21 2015
%E Corrected and extended by _Jon E. Schoenfield_, Apr 23 2015