A272573 Start a spiral of numbers on a hexagonal tiling, with the initial hexagon as a(1) = 1. a(n) is the smallest positive integer not equal to or previously adjacent to its neighbors.

1, 2, 3, 4, 5, 6, 7, 4, 6, 8, 5, 9, 8, 10, 2, 11, 3, 10, 11, 12, 13, 9, 12, 7, 13, 14, 1, 11, 13, 15, 9, 16, 14, 7, 16, 17, 15, 1, 16, 18, 7, 17, 19, 20, 1, 17, 18, 19, 9, 21, 3, 20, 10, 22, 4, 15, 21, 23, 5, 22, 23, 10, 21, 6, 22, 24, 25, 2, 14, 22, 25, 26, 3

Offset: 1

Author

Peter Kagey, May 03 2016

Keywords

• nonn

Comments

This is the hexagonal analog to A260643.

Examples

			Illustration of a(1) through a(8) and a(13):
    |     |     |      |       |       |       |        |     | 8 9 5
    |     |  3  | 4 3  |  4 3  |  4 3  |  4 3  |  4 3   |     |  4 3 8
  1 | 1 2 | 1 2 |  1 2 | 5 1 2 | 5 1 2 | 5 1 2 | 5 1 2  | ... | 5 1 2 6
    |     |     |      |       |  6    |  6 7  |  6 7 4 |     |  6 7 4
		

Links

• Peter Kagey, Table of n, a(n) for n = 1..10000
• Peter Kagey, Ruby program for computing sequence.

Crossrefs

Cf. A047932, A260643.