On two conjectures about pattern avoidance of cyclic permutations

Abstract

Let $\pi$ be a cyclic permutation that can be expressed in its one-line form as $\pi = \pi_1\pi_2 \cdot\cdot\cdot \pi_n$ and in its standard cycle form as $\pi = (c_1,c_2, ..., c_n)$ where $c_1=1$. Archer et al. introduced the notion of pattern avoidance of one-line and the standard cycle form for a cyclic permutation $\pi$, defined as both $\pi_1\pi_2 \cdot\cdot\cdot \pi_n$ and its standard cycle form $c_1c_2\cdot\cdot\cdot c_{n}$ avoiding a given pattern. Let $\mathcal{A}_n(\sigma_1,...,\sigma_k; \tau)$ denote the set of cyclic permutations in the symmetric group $S_n$ that avoid each pattern of $\{\sigma_1,...,\sigma_k\}$ in their one-line forms and avoid $\tau$ in their standard cycle forms. In this paper, we obtain some results about the cyclic permutations avoiding patterns in both one-line and cycle forms. In particular, we resolve two conjectures of Archer et al.