A358429 Construct a square spiral: a(n) is the sum of all adjacent terms a(k) in the spiral for k < n; a(1) = 0, a(2) = 1.

0, 1, 1, 2, 2, 4, 4, 9, 10, 11, 23, 25, 26, 54, 59, 63, 65, 134, 144, 152, 156, 321, 344, 374, 395, 406, 835, 894, 968, 1019, 1045, 2144, 2283, 2459, 2646, 2774, 2839, 5812, 6155, 6585, 7037, 7345, 7501, 15323, 16144, 17183, 18296, 19471, 20272

Offset: 1

Author

Abraham C Leventhal, Nov 15 2022

Keywords

• nonn

Comments

The terms "adjacent" to a(n) are terms in any of the 8 cells of the matrix which surround the cell containing a(n). See Github link for code (Python 3) which produces the matrix and sequence, and a picture of the matrix containing the first 49 terms.

Examples

			The spiral begins:
.
   65--63--59--54--26
    |               |
  134   2---2---1  25
    |   |       |   |
  ...   4   0---1  23
        |           |
        4---9--10--11
.
The last term shown is a(18) = 134 = 65 + 63 + 2 + 4, which is the sum of its adjacent earlier terms.
		

Links

• Abraham C Leventhal, Code and the 7 X 7 spiral, Github.

Crossrefs

Cf. A094767, A094769, A141481.