OFFSET
1,1
COMMENTS
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)
LINKS
R. H. Hardin, Table of n, a(n) for n = 1..25
EXAMPLE
Some solutions for n=3
.-2.-3..0.-2...-4..5.-6..2....5..2..1.-5...-2..5.-2..1....9.-6..9.-2
.-3..8.-5..7....5.-6..7.-3....2.-9..6.-2....5.-8..5.-4...-6..3.-6.-1
..0.-5..2.-4...-6..7.-8..4....1..6.-3.-1...-2..5.-2..1....9.-6..9.-2
.-2..7.-4..6....2.-3..4..0...-5.-2.-1..5....1.-4..1..0...-2.-1.-2.-5
CROSSREFS
KEYWORD
nonn
AUTHOR
R. H. Hardin Apr 15 2012
STATUS
approved