

A280027


Fill an infinite square array by following a spiral around the origin; in the central cell enter a(0)=1; thereafter, in the nth 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
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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:
.
742
 
13 11 239
 
234276146
.
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



