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A257339
Arrange numbers in a single clockwise spiral so that each number is relatively prime to its eight neighbors.
12
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, 53, 14, 15, 59, 27, 55, 39, 16, 61, 22, 51, 67, 18, 65, 24, 71, 26, 33, 32, 57, 73, 79, 83, 77, 85, 89, 97, 101, 28, 95, 34, 91, 38, 103, 107, 45, 109, 113, 20, 121
OFFSET
1,2
COMMENTS
Start with 1; always choose smallest number which has not yet appeared.
It is conjectured that every number appears.
LINKS
Jon E. Schoenfield and Reinhard Zumkeller, Table of n, a(n) for n = 1..100000 (First 10000 terms from Jon E. Schoenfield)
Jon E. Schoenfield, Illustration of initial terms
Jon E. Schoenfield, Graph of first 18000 terms
CROSSREFS
Cf. A257111 (first differences), A257455 (putative inverse).
Indices of primes and prime powers: A257457 and A257458.
Sequence in context: A102454 A232640 A085790 * A210882 A117120 A181095
KEYWORD
nonn
AUTHOR
N. J. A. Sloane, Apr 21 2015
EXTENSIONS
Corrected and extended by Jon E. Schoenfield, Apr 23 2015
STATUS
approved