Sets of Flattened Partitions with Forbidden Patterns
Olivia Nabawanda
Department of Mathematics
Makerere University
P. O. Box 7062
Kampala
Uganda
Fanja Rakotondrajao
Département de Mathématiques et Informatique
Université d'Antananarivo, Antananarivo
Antananarivo
Madagascar
Abstract:
The study of pattern avoidance in permutations, and specifically in
flattened partitions is an active area of current research. In this
paper, we count the number of distinct flattened partitions over [n]
avoiding a single pattern, as well as a pair of two patterns. Several
counting sequences, namely Catalan numbers, powers of two, Fibonacci
numbers and Motzkin numbers arise. We also consider other combinatorial
statistics, namely runs and inversions, and establish some bijections
in situations where the statistics coincide.
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(Concerned with sequences
A000012
A000045
A000108
A001006
A011782
A028310.)
Received December 5 2020; revised version received January 1 2021.
Published in Journal of Integer Sequences,
January 2 2021.
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