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A183763
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Number of 2 X 2 nonsingular 0..n matrices with a(1,1) <= a(1,2) <= a(2,1) <= a(2,2).
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0
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1, 6, 19, 44, 89, 158, 263, 408, 606, 867, 1208, 1629, 2162, 2807, 3584, 4510, 5615, 6893, 8394, 10107, 12076, 14321, 16874, 19723, 22938, 26527, 30517, 34930, 39831, 45188, 51109, 57563, 64616, 72301, 80642, 89657, 99462, 110027, 121404, 133613
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OFFSET
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1,2
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COMMENTS
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Singular matrices = binomial(n+4,4) - a(n).
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LINKS
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EXAMPLE
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All solutions for n=2:
..0..1....0..2....1..1....0..1....1..2....0..1
..1..1....2..2....1..2....2..2....2..2....1..2
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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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