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

1,2

Comments

This is the hexagonal analog to A260643.

Links

Peter Kagey, Table of n, a(n) for n = 1..10000

Peter Kagey, Ruby program for computing sequence.

Example

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

Crossrefs

Cf. A047932, A260643.

Sequence in context: A138221 A038388 A366392 * A328477 A332230 A319999

Adjacent sequences: A272570 A272571 A272572 * A272574 A272575 A272576

Keyword

nonn

Author

Peter Kagey, May 03 2016

Status

approved