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%I #4 Apr 20 2012 06:23:22
%S 264,3038,35014,404214,4673910,54129486,627846218,7293174926,
%T 84839745786,988267636274,11526926036602,134612671646418,
%U 1573840216457142,18420681939043482,215818650878928686,2530919496941096390
%N Number of (n+1)X(n+1) -11..11 symmetric matrices with every 2X2 subblock having sum zero and two, three or four distinct values
%C Symmetry and 2X2 block sums zero implies that the diagonal x(i,i) are equal modulo 2 and x(i,j)=(x(i,i)+x(j,j))/2*(-1)^(i-j)
%H R. H. Hardin, <a href="/A211718/b211718.txt">Table of n, a(n) for n = 1..33</a>
%e Some solutions for n=3
%e .-8..4..1..0...-3.-3.-3..0....8.-9..7.-5...-3.-3.-1..2...-2..6.-1.-1
%e ..4..0.-5..4...-3..9.-3..6...-9.10.-8..6...-3..9.-5..4....6-10..5.-3
%e ..1.-5.10.-9...-3.-3.-3..0....7.-8..6.-4...-1.-5..1..0...-1..5..0.-2
%e ..0..4.-9..8....0..6..0..3...-5..6.-4..2....2..4..0.-1...-1.-3.-2..4
%K nonn
%O 1,1
%A _R. H. Hardin_ Apr 20 2012
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