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A079510
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Triangle T(n,k) read by rows; related to number of preorders.
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1
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1, 0, 2, 0, 3, 6, 0, 0, 20, 24, 0, 0, 15, 130, 120, 0, 0, 0, 210, 924, 720, 0, 0, 0, 105, 2380, 7308, 5040, 0, 0, 0, 0, 2520, 26432, 64224, 40320, 0, 0, 0, 0, 945, 44100, 303660, 623376, 362880, 0, 0, 0, 0, 0, 34650, 705320, 3678840, 6636960, 3628800, 0, 0, 0, 0
(list; table; graph; refs; listen; history; internal format)
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OFFSET
| 2,3
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COMMENTS
| There are only m nonzero entries in the m-th column.
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REFERENCES
| G. Kreweras, Les preordres totaux compatibles avec un ordre partiel. Math. Sci. Humaines No. 53 (1976), 5-30. (The array on page 29.)
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EXAMPLE
| 1; 0,2; 0,3,6; 0,0,20,24; 0,0,15,130,120; ...
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PROG
| (PARI) T(n, k)=if(k<=1|k>n, n==1&k==1, n*(T(n-1, k-1)+T(n-2, k-1)))
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CROSSREFS
| A rearrangement of the triangle in A008306. - Benoit Cloitre, Jan 27, 2003.
Sequence in context: A061151 A094720 A155800 * A011120 A194737 A071089
Adjacent sequences: A079507 A079508 A079509 * A079511 A079512 A079513
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KEYWORD
| nonn,tabl
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AUTHOR
| N. J. A. Sloane (njas(AT)research.att.com), Jan 21 2003
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EXTENSIONS
| Recurrence and more terms from Michael Somos, Jan 23 2003
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