A363247 a(0) = 0. a(n) = the smallest nonnegative integer, excluding a(n-1), not occurring in all occurrences of a(n-1)'s eight neighbors thus far in a square spiral.

0, 1, 2, 3, 4, 1, 5, 2, 4, 5, 3, 6, 0, 7, 1, 8, 0, 9, 2, 8, 6, 4, 7, 8, 10, 0, 11, 1, 10, 2, 11, 4, 12, 2, 13, 3, 9, 5, 12, 3, 14, 0, 15, 1, 14, 5, 13, 4, 15, 2, 16, 1, 17, 0, 18, 1, 19, 0, 20, 1, 21, 0, 22, 1, 23, 0, 24, 1, 25, 0, 26, 1, 27, 0, 28, 2, 17, 3

Offset: 0

Author

Gavin Lupo, May 24 2023

Keywords

• nonn

Examples

			The spiral begins:
  0---8---1---7---0
  |               |
  9   4---3---2   6
  |   |       |   |
  2   1   0---1   3   .
  |   |           |   .
  8   5---2---4---5   .
  |                   |
  6---4---7---8---10--0
a(0) = 0
a(1) = 1. Smallest integer that's not a neighbor to every 0 = 1.
a(2) = 2. Smallest integer that's not a neighbor to every 1 = 2.
a(3) = 3. Smallest integer that's not a neighbor to every 2 = 3.
a(4) = 4. Smallest integer that's not a neighbor to every 3 = 4.
a(5) = 1. Smallest integer that's not a neighbor to every 4 = 1.
		

Links

• Scott R. Shannon, Table of n, a(n) for n = 0..10000
• Scott R. Shannon, Image of the first 10000 terms on the square spiral. The value colors are scaled across the spectrum from red to violet to show their relative size. Zoom in to see the numbers.

Crossrefs

Cf. A275609, A358048.