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

1,2

Links

Table of n, a(n) for n=1..20.

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

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

Crossrefs

Cf. A000108.

Sequence in context: A152637 A152645 A360386 * A324075 A193936 A226440

Adjacent sequences: A054870 A054871 A054872 * A054874 A054875 A054876

Keyword

nonn

Author

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

Status

approved