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..210
FORMULA
Empirical: a(n) = 5*a(n-1) +6*a(n-2) -66*a(n-3) +32*a(n-4) +343*a(n-5) -396*a(n-6) -874*a(n-7) +1475*a(n-8) +1066*a(n-9) -2702*a(n-10) -373*a(n-11) +2577*a(n-12) -367*a(n-13) -1195*a(n-14) +320*a(n-15) +210*a(n-16) -60*a(n-17)
EXAMPLE
Some solutions for n=3
..4.-2..4..0....6.-3..0.-6....1..3..1.-2....4..2..4.-3....9.-2..9.-2
.-2..0.-2.-2...-3..0..3..3....3.-7..3.-2....2.-8..2.-3...-2.-5.-2.-5
..4.-2..4..0....0..3.-6..0....1..3..1.-2....4..2..4.-3....9.-2..9.-2
..0.-2..0.-4...-6..3..0..6...-2.-2.-2..3...-3.-3.-3..2...-2.-5.-2.-5
CROSSREFS
KEYWORD
nonn
AUTHOR
R. H. Hardin Apr 15 2012
STATUS
approved