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) +11*a(n-2) -60*a(n-3) -34*a(n-4) +375*a(n-5) -53*a(n-6) -1270*a(n-7) +601*a(n-8) +2541*a(n-9) -1636*a(n-10) -3075*a(n-11) +2204*a(n-12) +2210*a(n-13) -1562*a(n-14) -875*a(n-15) +530*a(n-16) +150*a(n-17) -60*a(n-18)
EXAMPLE
Some solutions for n=3
..8.-2..8.-3....5.-7.-1.-7....5.-1..5.-2...-1..4..4..4....3.-5..3.-5
.-2.-4.-2.-3...-7..9.-1..9...-1.-3.-1.-2....4.-7.-1.-7...-5..7.-5..7
..8.-2..8.-3...-1.-1.-7.-1....5.-1..5.-2....4.-1..9.-1....3.-5..3.-5
.-3.-3.-3.-2...-7..9.-1..9...-2.-2.-2.-1....4.-7.-1.-7...-5..7.-5..7
CROSSREFS
KEYWORD
nonn
AUTHOR
R. H. Hardin Apr 15 2012
STATUS
approved