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A211818
Number of (n+1)X(n+1) -10..10 symmetric matrices with every 2X2 subblock having sum zero and three or four distinct values
0
188, 1702, 15334, 138130, 1242978, 11177174, 100431854, 901725738, 8089235074, 72498715894, 649077462926, 5804421919322, 51840849262274, 462375098375406, 4118031964300046, 36620792527293818
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
..6..2..5..2..-10..9-10..3....9.-6..2.-5....9.-2..4.-2...-8..1.-3.-1
..2-10..3-10....9.-8..9.-2...-6..3..1..2...-2.-5..3.-5....1..6.-4..8
..5..3..4..3..-10..9-10..3....2..1.-5..2....4..3.-1..3...-3.-4..2.-6
..2-10..3-10....3.-2..3..4...-5..2..2..1...-2.-5..3.-5...-1..8.-6.10
CROSSREFS
Sequence in context: A073586 A064115 A185241 * A204071 A089273 A035832
KEYWORD
nonn
AUTHOR
R. H. Hardin Apr 21 2012
STATUS
approved