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%I #3 Apr 20 2012 06:22:42
%S 231,2333,23349,232503,2302953,22704347,222873481,2179177539,
%T 21229916021,206133137263,1995258434861
%N Number of (n+1)X(n+1) -11..11 symmetric matrices with every 2X2 subblock having sum zero and one, 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)
%e Some solutions for n=3
%e .-1..2.-6..5....1.-4..3..1....1..3..0..4...-5..6.-5..7...-4..2.-6..4
%e ..2.-3..7.-6...-4..7.-6..2....3.-7..4.-8....6.-7..6.-8....2..0..4.-2
%e .-6..7-11.10....3.-6..5.-1....0..4.-1..5...-5..6.-5..7...-6..4.-8..6
%e ..5.-6.10.-9....1..2.-1.-3....4.-8..5.-9....7.-8..7.-9....4.-2..6.-4
%K nonn
%O 1,1
%A _R. H. Hardin_ Apr 20 2012
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