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Search: id:A049055
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| A049055 |
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Triangle read by rows, giving T(n,k) = number of k-member minimal ordered covers of a labeled n-set (n > 0, k > 0). |
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+0
3
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| 1, 1, 1, 2, 1, 12, 6, 1, 50, 132, 24, 1, 180, 1830, 1560, 120, 1, 602, 20460, 60960, 20520, 720, 1, 1932, 201726, 1856400, 2047920, 302400, 5040, 1, 6050, 1832292, 48550824, 155801520, 72586080, 4979520, 40320, 1, 18660, 15717750
(list; graph; listen)
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OFFSET
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0,4
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REFERENCES
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R. J. Clarke, Covering a set by subsets, Discrete Math., 81 (1990), 147-152.
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EXAMPLE
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1; 1; 1,2; 1,12,6; 1,50,132,24; ...
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PROGRAM
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(PARI) {T(n, k)=sum(i=0, k, (-1)^i*binomial(k, i)*(2^k-1-i)^n)} /* Michael Somos Oct 16 2006 */
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CROSSREFS
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Row sums are A049056.
Sequence in context: A107722 A167128 A048743 this_sequence A008285 A119274 A066991
Adjacent sequences: A049052 A049053 A049054 this_sequence A049056 A049057 A049058
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KEYWORD
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nonn,tabf,easy,nice
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AUTHOR
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N. J. A. Sloane (njas(AT)research.att.com), Michael Somos
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