A263886 Number of permutations of [n] containing exactly two occurrences of the consecutive pattern 132.

3, 56, 753, 9024, 104814, 1228608, 14824314, 185991936, 2438459325, 33476112000, 481470208575, 7252002478080, 114295913943660, 1882806417303552, 32377593994012260, 580478495476948992, 10835925949596420135, 210343353555466229760, 4240673559279540077085

Offset

5,1

Links

Alois P. Heinz, Table of n, a(n) for n = 5..200

Formula

a(n) = A197365(n,2).

Example

a(5) = 3: 13254, 14253, 15243.
a(6) = 56: 124365, 125364, 126354, ..., 613254, 614253, 615243.
a(7) = 753: 1235476, 1236475, 1237465, ..., 7613254, 7614253, 7615243.
a(8) = 9024: 12346587, 12347586, 12348576, ..., 87613254, 87614253, 87615243.

Maple

b:= proc(u, o, t) option remember; series(`if`(u+o=0, 1,
      add(b(u-j, o+j-1, 0)*`if`(j<=t, x, 1), j=1..u)+
      add(b(u+j-1, o-j, j-1), j=1..o)), x, 3)
    end:
a:= n-> coeff(b(n, 0$2), x, 2):
seq(a(n), n=5..30);

Crossrefs

Column k=2 of A197365.

Sequence in context: A280805 A198184 A262398 * A160876 A241136 A202029

Adjacent sequences: A263883 A263884 A263885 * A263887 A263888 A263889

Keyword

nonn

Author

Alois P. Heinz, Oct 28 2015

Status

approved