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A054873
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Number of (S_5 67)-avoiding permutations.
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1
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1, 2, 6, 24, 120, 720, 5040, 40320, 357840, 3427200, 34685280, 365541120, 3971615760, 44181889920, 500788985760, 5763231048960, 67163932069920, 791030794095360, 9400660122813120, 112587818898562560
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,2
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REFERENCES
| E. Barcucci, A. Del Lungo, E. Pergola, R. Pinzani, Permutations avoiding an increasing number of length-increasing forbidden subsequences, Discrete MAthematics and Theoretical Computer Science 4, 2000, 31-44
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LINKS
| E. Barcucci, A. Del Lungo, E. Pergola and R. Pinzani, Permutations avoiding an increasing number of length-increasing forbidden subsequences
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FORMULA
| f := (x, j)->1-(j+1)*x- sqrt(1-2*(j+1)*x+(j-1)^2*x^2); t := (x, j)->sum(k!*x^k, k=1..(j-1)); s := (x, j)->x^(j-2)*(j-1)!*(f(x, j))/(2)+ t(x, j); j := 6
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CROSSREFS
| Cf. A000108.
Sequence in context: A152644 A152637 A152645 * A193936 A072132 A066459
Adjacent sequences: A054870 A054871 A054872 * A054874 A054875 A054876
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KEYWORD
| nonn
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AUTHOR
| Elisa Pergola (elisa(AT)dsi.unifi.it), May 26 2000
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