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A261212 Maximum number of 1's in an fully symmetrical n X n binary matrix with no three 1's adjacent in a line along a row, column or diagonally.

%I A261212 #22 Aug 19 2015 15:20:17
%S A261212 1,4,4,8,16,20,25,36,41,48,64,72,81,100,109,120,144,156,173,196,213,
%T A261212 228,256,272,300,324,349,368,401,424,457,484
%N A261212 Maximum number of 1's in an fully symmetrical n X n binary matrix with no three 1's adjacent in a line along a row, column or diagonally.
%C A261212 Fully symmetrical refers to the four symmetry axes: horizontal, vertical and two diagonal.
%C A261212 Note that a(3k+2) = 4*(1+k)^2, for k=0,...,8, but a(29) = 401.
%H A261212 Giovanni Resta, <a href="/A261212/a261212.pdf">Illustration of a(6)-a(30)</a>
%F A261212 a(n) <= A181018(n).
%F A261212 a(3k+2) >= 4*(k+1)^2.
%e A261212 For n=4, the matrix is
%e A261212 0 1 0
%e A261212 1 0 1
%e A261212 0 1 0
%e A261212 For n=6, the matrix is
%e A261212 1 1 0 0 1 1
%e A261212 1 0 1 1 0 1
%e A261212 0 1 0 0 1 0
%e A261212 0 1 0 0 1 0
%e A261212 1 0 1 1 0 1
%e A261212 1 1 0 0 1 1
%Y A261212 Cf. A181018.
%K A261212 nonn
%O A261212 1,2
%A A261212 _V.J. Pohjola_ and _Giovanni Resta_, Aug 12 2015