A165544 Number of permutations of length n which avoid the patterns 4123 and 3412.

1, 1, 2, 6, 22, 89, 381, 1696, 7781, 36572, 175277, 853410, 4209376, 20988122, 105611537, 535638107

Offset

0,3

Links

Table of n, a(n) for n=0..15.

Darla Kremer and Wai Chee Shiu, Finite transition matrices for permutations avoiding pairs of length four patterns, Discrete Math. 268 (2003), 171-183. MR1983276 (2004b:05006). See Table 1.

Wikipedia, Permutation classes avoiding two patterns of length 4.

Example

There are 22 permutations of length 4 which avoid these two patterns, so a(4)=22.

Crossrefs

Sequence in context: A165543 A049123 A200753 * A150268 A369439 A165545

Adjacent sequences: A165541 A165542 A165543 * A165545 A165546 A165547

Keyword

nonn,more

Author

Vincent Vatter, Sep 21 2009

Extensions

The 6th term should be 381, not 3381. Sorry about that. - Vincent Vatter, Oct 01 2010

a(0)=1 prepended by Alois P. Heinz, Dec 09 2015

a(13)-a(15) from Lars Blomberg, Apr 26 2018

Status

approved