OFFSET
1,1
COMMENTS
Symmetry and 2 X 2 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) = 23*a(n-1) - 132*a(n-2).
Conjectures from Colin Barker, Jul 19 2018: (Start)
G.f.: x*(265 - 3036*x) / ((1 - 11*x)*(1 - 12*x)).
a(n) = 11^(1+n) + 12^(1+n).
(End)
EXAMPLE
Some solutions for n=3.
..4..0.-3..1...-1..0..5.-5...-5.-1..3..6...11.-3.10.-9..-10..4.-7..0
..0.-4..7.-5....0..1.-6..6...-1..7.-9..0...-3.-5.-2..1....4..2..1..6
.-3..7-10..8....5.-6.11-11....3.-9.11.-2...10.-2..9.-8...-7..1.-4.-3
..1.-5..8.-6...-5..6-11.11....6..0.-2.-7...-9..1.-8..7....0..6.-3.10
CROSSREFS
KEYWORD
nonn
AUTHOR
R. H. Hardin, Apr 20 2012
STATUS
approved