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) +9*a(n-2) -80*a(n-3) +9*a(n-4) +535*a(n-5) -425*a(n-6) -1941*a(n-7) +2321*a(n-8) +4142*a(n-9) -6337*a(n-10) -5243*a(n-11) +10073*a(n-12) +3703*a(n-13) -9603*a(n-14) -1139*a(n-15) +5360*a(n-16) -87*a(n-17) -1632*a(n-18) +123*a(n-19) +238*a(n-20) -18*a(n-21) -12*a(n-22)
EXAMPLE
Some solutions for n=3
..3..0..3..0....5.-1.-3.-1...-1..3..1..0....1..3..2..3...10.-6.10.-2
..0.-3..0.-3...-1.-3..7.-3....3.-5..1.-2....3.-7..2.-7...-6..2.-6.-2
..3..0..3..0...-3..7-11..7....1..1..3.-2....2..2..3..2...10.-6.10.-2
..0.-3..0.-3...-1.-3..7.-3....0.-2.-2..1....3.-7..2.-7...-2.-2.-2.-6
CROSSREFS
KEYWORD
nonn
AUTHOR
R. H. Hardin Apr 20 2012
STATUS
approved