A363938 Lexicographically earliest sequence of numbers in a hexagonal spiral such that their neighbors have no common prime factor.

1, 2, 3, 4, 5, 6, 7, 9, 11, 13, 8, 17, 15, 19, 12, 23, 25, 29, 10, 31, 14, 27, 16, 21, 37, 33, 26, 41, 22, 35, 43, 47, 18, 49, 24, 53, 39, 20, 51, 55, 28, 59, 61, 32, 45, 34, 67, 57, 40, 63, 71, 36, 65, 38, 73, 79, 30, 83, 77, 46, 89, 69, 91, 58, 81, 85, 87

Offset: 1

Author

Carole Dubois, Jun 29 2023

Keywords

• nonn

Examples

			a(11) = 8 because the neighbors of the 11th hexagon are 3, 13, 17, 21, 33, 37, which do not have any common prime divisor with 8.
		

Links

• Carole Dubois, Table of n, a(n) for n = 1..4999
• Carole Dubois, Hexagonal spiral for A363938.
• Carole Dubois, Scatterplot of A363938(n)
• Carole Dubois, Hexagons with spiral

Crossrefs

Cf. A000384, A003458, A014105, A056105, A363765.