A257339 Arrange numbers in a single clockwise spiral so that each number is relatively prime to its eight neighbors.

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. A064413, A257321-A257340.

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

Adjacent sequences: A257336 A257337 A257338 * A257340 A257341 A257342

Keyword

nonn

Author

N. J. A. Sloane, Apr 21 2015

Extensions

Corrected and extended by Jon E. Schoenfield, Apr 23 2015

Status

approved