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A358429 Construct a square spiral: a(n) is the sum of all adjacent terms a(k) in the spiral for k < n; a(1) = 0, a(2) = 1.

%I A358429 #17 Dec 06 2022 09:24:25
%S A358429 0,1,1,2,2,4,4,9,10,11,23,25,26,54,59,63,65,134,144,152,156,321,344,
%T A358429 374,395,406,835,894,968,1019,1045,2144,2283,2459,2646,2774,2839,5812,
%U A358429 6155,6585,7037,7345,7501,15323,16144,17183,18296,19471,20272
%N A358429 Construct a square spiral: a(n) is the sum of all adjacent terms  a(k) in the spiral for k < n; a(1) = 0, a(2) = 1.
%C A358429 The terms "adjacent" to a(n) are terms in any of the 8 cells of the matrix which surround the cell containing a(n). See Github link for code (Python 3) which produces the matrix and sequence, and a picture of the matrix containing the first 49 terms.
%H A358429 Abraham C Leventhal, <a href="https://github.com/Abraham-Leventhal/Mathstuff">Code and the 7 X 7 spiral</a>, Github.
%e A358429 The spiral begins:
%e A358429 .
%e A358429    65--63--59--54--26
%e A358429     |               |
%e A358429   134   2---2---1  25
%e A358429     |   |       |   |
%e A358429   ...   4   0---1  23
%e A358429         |           |
%e A358429         4---9--10--11
%e A358429 .
%e A358429 The last term shown is a(18) = 134 = 65 + 63 + 2 + 4, which is the sum of its adjacent earlier terms.
%Y A358429 Cf. A094767, A094769, A141481.
%K A358429 nonn
%O A358429 1,4
%A A358429 _Abraham C Leventhal_, Nov 15 2022