A280027 Fill an infinite square array by following a spiral around the origin; in the central cell enter a(0)=1; thereafter, in the n-th cell, enter the sum of the entries of those earlier cells that can be seen from that cell.

1, 1, 2, 4, 7, 13, 23, 42, 76, 146, 239, 441, 852, 1389, 2536, 4971, 9832, 15312, 27964, 54801, 108787, 169086, 308758, 603612, 1201837, 2397202, 3656904, 6687912, 13067709, 25998877, 51918269, 79176868, 144799285, 282915788, 562653823, 1124083053, 2246758839

Offset: 0

Author

N. J. A. Sloane, Dec 24 2016

Keywords

• nonn
• tabl

Comments

The spiral track being used here is the same as in A274640, except that the starting cell here is indexed 0 (as in A274641).

The central cell gets index 0 (and we fill it in with the value a(0)=1).

"Can be seen from" means "that are on the same row, column, diagonal, or antidiagonal as".

Examples

			The central portion of the spiral is:
.
     7----4----2
     |         |
    13    1----1  239
     |             |
    23---42---76--146
.
After the terms a(0) to a(8) of the spiral have been filled in, the next cell contains 76+42+23+1+4 = 146 = a(9).
		

Links

• Lars Blomberg, Table of n, a(n) for n = 0..3384

Crossrefs

Cf. A274640, A274641, A278180.

Extensions

More terms from Lars Blomberg, Dec 25 2016