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

Author

Benoit Cloitre, May 27 2003

Keywords

• nonn

Links

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

Crossrefs

Column k=2 of A263771.

Programs

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 *)

PARI

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

Formula

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