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A054873 Number of (S_5 67)-avoiding permutations. 1

%I

%S 1,2,6,24,120,720,5040,40320,357840,3427200,34685280,365541120,

%T 3971615760,44181889920,500788985760,5763231048960,67163932069920,

%U 791030794095360,9400660122813120,112587818898562560

%N Number of (S_5 67)-avoiding permutations.

%H Elena Barcucci, Alberto Del Lungo, Elisa Pergola, Renzo Pinzani, <a href="https://hal.inria.fr/hal-00958943">Permutations avoiding an increasing number of length-increasing forbidden subsequences</a>, Discrete MAthematics and Theoretical Computer Science 4, 2000, 31-44

%F 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

%Y Cf. A000108.

%K nonn

%O 1,2

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

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Last modified July 26 14:45 EDT 2021. Contains 346294 sequences. (Running on oeis4.)