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A182062
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T(n,k) = C(n+1-k,k)*k!*(n-k)!, the number of ways for k men and n-k women to form a queue in which no man is next to another man.
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1
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1, 1, 1, 2, 2, 0, 6, 6, 2, 0, 24, 24, 12, 0, 0, 120, 120, 72, 12, 0, 0, 720, 720, 480, 144, 0, 0, 0, 5040, 5040, 3600, 1440, 144, 0, 0, 0, 40320, 40320, 30240, 14400, 2880, 0, 0, 0, 0, 362880, 362880, 282240, 151200, 43200, 2880, 0, 0, 0, 0, 3628800, 3628800
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OFFSET
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0,4
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COMMENTS
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Triangle T(n,k), 0<=k<=n, is readily derived since there are C(n+1-k,k) ways to form a sequence of k zeros and n-k ones in which no zeros are consecutive and there are k!(n-k)! ways to permute k labeled zeros and n-k labeled ones. This triangle contains several known sequences, notably A000142 (factorial numbers), A062119 (number of multiplications performed in a determinant), and A010796.
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LINKS
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FORMULA
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binomial(n+1-k,k)*k!*(n-k)!
G.f. (fixed k): (1-k)*hypergeom([1, 1-k, 2-k],[2-2*k],t)*GAMMA(1-k)^2/GAMMA(2-2*k)
T(n,k)=(n+2-2k)*T(n-1,k-1)
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EXAMPLE
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T(4,2)=12 since there are 12 ways to line up two men {M,m} and two women {W,w} so that no man is next to another man, namely, MWmw, MWwm, MwmW, MwWm, mWMw, mWwM, mwMW, mwWM, WMwm, WmwM, wMWm, and wmWM.
Triangle T(n,k) begins
1,
1, 1,
2, 2, 0,
6, 6, 2, 0,
24, 24, 12, 0, 0,
120, 120, 72, 12, 0, 0,
720, 720, 480, 144, 0, 0, 0,
5040, 5040, 3600, 1440, 144, 0, 0, 0,
40320, 40320, 30240, 14400, 2880, 0, 0, 0, 0,
362880,362880,282240,151200,43200,2880,0,0,0,0,
3628800,3628800,2903040,1693440,604800,86400,0,0,0,0,0
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MAPLE
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seq(seq(binomial(n+1-k, k)*k!*(n-k)!, k=0..n), n=0..10);
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MATHEMATICA
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Flatten[Table[Binomial[n+1-k, k]k!(n-k)!, {n, 0, 10}, {k, 0, n}]] (* Harvey P. Dale, Jul 15 2012 *)
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CROSSREFS
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KEYWORD
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AUTHOR
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STATUS
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approved
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