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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. 5
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 (list; table; graph; refs; listen; history; text; internal format)
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

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Last modified May 27 21:52 EDT 2020. Contains 334671 sequences. (Running on oeis4.)