On minimal pattern-containing inversion sequences

Abstract

We introduce the notion of minimal inversion sequences for a pattern $\ddot{I}$, which form the smallest set of inversion sequences whose avoidance is equivalent to the avoidance of $\ddot{I}$ for inversion sequences. We give a characterization of $\ddot{I}$-minimal inversion sequences based on the occurrences of the pattern $\ddot{I}$ they contain, and use it to find upper and lower bounds on the lengths of $\ddot{I}$-minimal inversion sequences. We provide some enumerative results on the exact number of minimal inversion sequences for some patterns, through a bijection with increasing trees, and some exhaustive generation. Lastly, we enumerate inversion sequences which are equal to their reduction, and find an interesting connection with poly-Bernoulli numbers.

20 pages, 3 figures, 3 tables