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) = 3*a(n-1) +20*a(n-2) -64*a(n-3) -172*a(n-4) +598*a(n-5) +826*a(n-6) -3213*a(n-7) -2390*a(n-8) +10954*a(n-9) +4103*a(n-10) -24660*a(n-11) -3463*a(n-12) +36968*a(n-13) -524*a(n-14) -36330*a(n-15) +4151*a(n-16) +22474*a(n-17) -3786*a(n-18) -8144*a(n-19) +1410*a(n-20) +1540*a(n-21) -180*a(n-22) -120*a(n-23)
EXAMPLE
Some solutions for n=3
..1.-2..1..1....5.-5..0.-5....2..1..1..1...-8..6.-4..6....1..1..1.-2
.-2..3.-2..0...-5..5..0..5....1.-4..2.-4....6.-4..2.-4....1.-3..1..0
..1.-2..1..1....0..0.-5..0....1..2..0..2...-4..2..0..2....1..1..1.-2
..1..0..1.-3...-5..5..0..5....1.-4..2.-4....6.-4..2.-4...-2..0.-2..3
CROSSREFS
KEYWORD
nonn
AUTHOR
R. H. Hardin Apr 12 2012
STATUS
approved