OFFSET
0,3
COMMENTS
Two-clumped permutations are (3-51-2-4, 3-51-4-2, 2-4-51-3, 4-2-51-3)-avoiding permutations. Co-two-clumped permutations are (3-15-2-4, 3-15-4-2, 2-4-15-3, 4-2-15-3)-avoiding permutations. Thus, this sequence enumerates permutations that avoid all these eight patterns.
a(n) is also the number of strong (=generic) rectangulations of size n whose strong poset is totally ordered.
LINKS
Andrei Asinowski, Jean Cardinal, Stefan Felsner, and Éric Fusy, Combinatorics of rectangulations: Old and new bijections, arXiv:2402.01483 [math.CO], 2024, page 29.
CROSSREFS
KEYWORD
nonn
AUTHOR
Andrei Asinowski, Sep 02 2024
STATUS
approved