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A181201
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a(n) = 0!*1!*2!*(3*n)!*3*n*(n-1) / ((n)!*(n+1)!*(n+2)!).
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1
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0, 30, 756, 16632, 360360, 7876440, 174594420, 3926434512, 89492111280, 2064420294300, 48134517631200, 1133012491934400, 26895067957892160, 643240375326254160, 15487976684184750900, 375182135475713517600
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OFFSET
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1,2
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COMMENTS
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(Empirical) Number of n X 3 matrices containing a defective permutation of 1..3*n in strictly increasing order rowwise and columnwise, with one permutation value omitted and one repeated (see example).
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LINKS
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EXAMPLE
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Some solutions for 4 X 3
..1..3..4....1..4..6....1..4..6....1..2..8....1..2..7....1..2..8....1..2..3
..2..6..9....2..5..7....2..7..9....3..4..9....2..5..9....2..5..9....2..6..7
..7..8.10....3..9.11....3..8.11....5..7.11....3..8.11....3..6.11....5..8..9
.10.11.12....5.10.12....7.10.12....6..9.12....6.10.12....7.10.12...10.11.12
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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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