A082970 Number of permutations of length n containing 2 occurrences of 132.

4, 23, 107, 464, 1950, 8063, 33033, 134576, 546312, 2212550, 8946454, 36134656, 145831270, 588199815, 2371435125, 9557736480, 38511326040, 155143873170, 624899673690, 2516678580000, 10134353299980, 40805797511622

Offset

4,1

Links

Table of n, a(n) for n=4..25.

T. Mansour and A. Vainshtein, Counting occurrences of 132 in a permutation, arXiv:math/0105073 [math.CO], 2001.

Formula

a(n) = C(2*n-6,n-2)*(n^3+17*n^2-80*n+80)/(2n(n-1)).

Mathematica

Table[Binomial[2n-6, n-2] (n^3+17n^2-80n+80)/(2n(n-1)), {n, 4, 30}] (* Harvey P. Dale, Dec 25 2018 *)

Prog

(PARI) a(n)=binomial(2*n-6, n-2)*(n^3+17*n^2-80*n+80)/2/n/(n-1)

Crossrefs

Column k=2 of A263771.

Sequence in context: A038381 A241777 A321614 * A197868 A017973 A306669

Adjacent sequences: A082967 A082968 A082969 * A082971 A082972 A082973

Keyword

nonn

Author

Benoit Cloitre, May 27 2003

Status

approved