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A211717
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Number of (n+1)X(n+1) -11..11 symmetric matrices with every 2X2 subblock having sum zero and one, three or four distinct values
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0
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231, 2333, 23349, 232503, 2302953, 22704347, 222873481, 2179177539, 21229916021, 206133137263, 1995258434861
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OFFSET
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1,1
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COMMENTS
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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)
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LINKS
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EXAMPLE
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Some solutions for n=3
.-1..2.-6..5....1.-4..3..1....1..3..0..4...-5..6.-5..7...-4..2.-6..4
..2.-3..7.-6...-4..7.-6..2....3.-7..4.-8....6.-7..6.-8....2..0..4.-2
.-6..7-11.10....3.-6..5.-1....0..4.-1..5...-5..6.-5..7...-6..4.-8..6
..5.-6.10.-9....1..2.-1.-3....4.-8..5.-9....7.-8..7.-9....4.-2..6.-4
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CROSSREFS
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KEYWORD
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nonn
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AUTHOR
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STATUS
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approved
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