A177470 Number of permutations of order n avoiding the consecutive pattern 11'22'.

1, 1, 2, 6, 18, 70, 300, 1435, 7910, 47376, 316008, 2314158, 18331236, 158024724, 1462752720, 14497475850, 153488070450, 1724035906450, 20515906356660, 257720354712106, 3406481187714176, 47293781230517640, 687760952277462336, 10456003715906638162, 165890170459303164420

Offset

0,3

Comments

To avoid 11'22' means not to have four consecutive letters such that the first letter is less than the third one and the second letter is less than the fourth one.

Links

Table of n, a(n) for n=0..24.

S. Kitaev, Introduction to partially ordered patterns, Discrete Applied Mathematics 155 (2007), 929-944.

Rémy Sigrist, C program

Prog

(C) // See Links section.

Crossrefs

Cf. A117156, A177471, A177472, A177473, A177475, A177476, A177477, A177478, A177479, A177480, A177481, A177482, A177483, A177484, A376694.

Sequence in context: A006389 A030269 A150082 * A060181 A131281 A264036

Adjacent sequences: A177467 A177468 A177469 * A177471 A177472 A177473

Keyword

nonn

Author

Signy Olafsdottir (signy06(AT)ru.is), May 09 2010

Extensions

a(0) = 1 and a(10)-a(16) from Rémy Sigrist, Mar 13 2023

Edited and a(17)-a(24) added by Max Alekseyev, Oct 01 2024

Status

approved