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

Author

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

Keywords

• nonn

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

• S. Kitaev, Introduction to partially ordered patterns, Discrete Applied Mathematics 155 (2007), 929-944.
• Rémy Sigrist, C program

Crossrefs

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

Programs

C

// See Links section.

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