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) = 4*a(n-1) +10*a(n-2) -56*a(n-3) -24*a(n-4) +321*a(n-5) -83*a(n-6) -968*a(n-7) +584*a(n-8) +1640*a(n-9) -1342*a(n-10) -1543*a(n-11) +1518*a(n-12) +750*a(n-13) -868*a(n-14) -166*a(n-15) +236*a(n-16) +12*a(n-17) -24*a(n-18)
EXAMPLE
Some solutions for n=3
..1..1..1.-3...-3..3..0..3...-1..0..0..1....2..2..2..1...-4..4.-4..4
..1.-3..1..1....3.-3..0.-3....0..1.-1..0....2.-6..2.-5....4.-4..4.-4
..1..1..1.-3....0..0..3..0....0.-1..1..0....2..2..2..1...-4..4.-4..4
.-3..1.-3..5....3.-3..0.-3....1..0..0.-1....1.-5..1.-4....4.-4..4.-4
CROSSREFS
KEYWORD
nonn
AUTHOR
R. H. Hardin Apr 06 2012
STATUS
approved