A054873 Number of (S_5 67)-avoiding permutations.

1, 2, 6, 24, 120, 720, 5040, 40320, 357840, 3427200, 34685280, 365541120, 3971615760, 44181889920, 500788985760, 5763231048960, 67163932069920, 791030794095360, 9400660122813120, 112587818898562560

Offset: 1

Author

Elisa Pergola (elisa(AT)dsi.unifi.it), May 26 2000

Keywords

• nonn

Links

• Elena Barcucci, Alberto Del Lungo, Elisa Pergola, Renzo Pinzani, Permutations avoiding an increasing number of length-increasing forbidden subsequences, Discrete Mathematics and Theoretical Computer Science 4, 2000, 31-44

Crossrefs

Cf. A000108.

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