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A211446
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Number of (n+1) X (n+1) -7..7 symmetric matrices with every 2 X 2 subblock having sum zero and three or four distinct values.
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1
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90, 548, 3296, 19844, 119260, 716592, 4303756, 25835124, 154970728, 928644692, 5557654436, 33210094112, 198105342332, 1179507539876, 7008630194584, 41558569591508, 245903742193060, 1451916609628912, 8554514693602716
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OFFSET
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1,1
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COMMENTS
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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).
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LINKS
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R. H. Hardin, Table of n, a(n) for n = 1..69
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EXAMPLE
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Some solutions for n=3
..4.-2..3.-4...-1.-3..0..3...-4.-1.-1.-1....0..2.-1.-2...-5..3..0..6
.-2..0.-1..2...-3..7.-4..1...-1..6.-4..6....2.-4..3..0....3.-1.-2.-4
..3.-1..2.-3....0.-4..1..2...-1.-4..2.-4...-1..3.-2.-1....0.-2..5..1
.-4..2.-3..4....3..1..2.-5...-1..6.-4..6...-2..0.-1..4....6.-4..1.-7
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CROSSREFS
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Sequence in context: A233638 A289792 A156738 * A203787 A203780 A295982
Adjacent sequences: A211443 A211444 A211445 * A211447 A211448 A211449
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KEYWORD
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nonn
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AUTHOR
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R. H. Hardin Apr 11 2012
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STATUS
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approved
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