|
%I #4 Apr 15 2012 11:14:09
%S 151,1211,9575,75219,586879,4554563,35183583,270747747,2076732739,
%T 15885966079,121240881187,923512887871,7023016209951,53333227033923,
%U 404532274018643,3065221230865231,23205080205698791,175535780415251539
%N Number of (n+1)X(n+1) -9..9 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)
%H R. H. Hardin, <a href="/A211555/b211555.txt">Table of n, a(n) for n = 1..25</a>
%e Some solutions for n=3
%e ..0.-2..1.-3...-3..5..3..1...-2..1..2..1....9.-1..6.-3....9.-4..5.-1
%e .-2..4.-3..5....5.-7.-1.-3....1..0.-3..0...-1.-7..2.-5...-4.-1..0.-4
%e ..1.-3..2.-4....3.-1..9.-5....2.-3..6.-3....6..2..3..0....5..0..1..3
%e .-3..5.-4..6....1.-3.-5..1....1..0.-3..0...-3.-5..0.-3...-1.-4..3.-7
%K nonn
%O 1,1
%A _R. H. Hardin_ Apr 15 2012
| 