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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.

%I A280027 #27 Dec 25 2016 23:16:18
%S A280027 1,1,2,4,7,13,23,42,76,146,239,441,852,1389,2536,4971,9832,15312,
%T A280027 27964,54801,108787,169086,308758,603612,1201837,2397202,3656904,
%U A280027 6687912,13067709,25998877,51918269,79176868,144799285,282915788,562653823,1124083053,2246758839
%N 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.
%C A280027 The spiral track being used here is the same as in A274640, except that the starting cell here is indexed 0 (as in A274641).
%C A280027 The central cell gets index 0 (and we fill it in with the value a(0)=1).
%C A280027 "Can be seen from" means "that are on the same row, column, diagonal, or antidiagonal as".
%H A280027 Lars Blomberg, <a href="/A280027/b280027.txt">Table of n, a(n) for n = 0..3384</a>
%e A280027 The central portion of the spiral is:
%e A280027 .
%e A280027      7----4----2
%e A280027      |         |
%e A280027     13    1----1  239
%e A280027      |             |
%e A280027     23---42---76--146
%e A280027 .
%e A280027 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).
%Y A280027 Cf. A274640, A274641, A278180.
%K A280027 nonn,tabl
%O A280027 0,3
%A A280027 _N. J. A. Sloane_, Dec 24 2016
%E A280027 More terms from _Lars Blomberg_, Dec 25 2016