Restricted growth function patterns and statistics

Abstract

A restricted growth function (RGF) of length n is a sequence w=w1w2…wn of positive integers such that w1=1 and wi≤1+max⁡{w1,…,wi−1} for i≥2. RGFs are of interest because they are in natural bijection with set partitions of {1,2,…,n}. An RGF w avoids another RGF v if there is no subword of w which standardizes to v. We study the generating functions ∑w∈Rn(v)qst(w) where Rn(v) is the set of RGFs of length n which avoid v and st(w) is any of the four fundamental statistics on RGFs defined by Wachs and White. These generating functions exhibit interesting connections with multiset permutations, integer partitions, and two-colored Motzkin paths, as well as noncrossing and nonnesting set partitions.