On Simsun and Double Simsun Permutations Avoiding a Pattern of Length Three

Wan-Chen Chuang, Sen-Peng Eu, Tung-Shan Fu +1

A permutation $\sigma \in {\mathfrak{S}}_n$ is simsun if for all $k$, the subword of $\sigma$ restricted to $\{1,...,k\}$ does not have three consecutive decreasing elements. The permutation $\sigma$…