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A211716
Number of (n+1)X(n+1) -11..11 symmetric matrices with every 2X2 subblock having sum zero and three or four distinct values
0
230, 2312, 23056, 228984, 2263896, 22292220, 218675604, 2137539096, 20825437008, 202270208796, 1958886321268, 18919069642800
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)
EXAMPLE
Some solutions for n=3
..4..3.-1.-6...-8..2.-8..2..-10..3.-4..0...-1..4.-3.-4...-7..8.-7..3
..3-10..8.-1....2..4..2..4....3..4.-3..7....4.-7..6..1....8.-9..8.-4
.-1..8.-6.-1...-8..2.-8..2...-4.-3..2.-6...-3..6.-5.-2...-7..8.-7..3
.-6.-1.-1..8....2..4..2..4....0..7.-6.10...-4..1.-2..9....3.-4..3..1
CROSSREFS
Sequence in context: A291617 A304389 A211711 * A251445 A251283 A251276
KEYWORD
nonn
AUTHOR
R. H. Hardin Apr 20 2012
STATUS
approved