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

0,3

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".

Links

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

Example

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).

Crossrefs

Cf. A274640, A274641, A278180.

Sequence in context: A078038 A190502 A048888 * A026724 A054163 A036256

Adjacent sequences: A280024 A280025 A280026 * A280028 A280029 A280030

Keyword

nonn,tabl

Author

N. J. A. Sloane, Dec 24 2016

Extensions

More terms from Lars Blomberg, Dec 25 2016

Status

approved