Set Partitions and Other Bell Number Enumerated Objects

TL;DR

This paper explores classes of set partitions and subexcedant functions counted by Bell numbers, introducing bijections and permutations that deepen understanding of Bell number enumerated objects.

Contribution

It introduces Bell permutations of the second kind, establishes bijections between different Bell number enumerated classes, and analyzes set partition statistics.

Findings

Bijections between Bell permutations of the first and second kind.

An involution interchanging merging blocks and successions.

Enumeration of distribution of set partition statistics.

Abstract

In this paper, we study classes of subexcedant functions enumerated by the Bell numbers and present bijections on set partitions. We present a set of permutations whose transposition arrays are the restricted growth functions, thus defining Bell permutations of the second kind. We describe a bijection between Bell permutations of the first kind (introduced by Ponti and Vajnovzski) and the second kind. We present two other Bell number enumerated classes of subexcedant functions. Further, we present bijections on set partitions, in particular, an involution that interchanges the set of merging blocks and the set of successions. We use the bijections to enumerate the distribution of these statistics over the set of set partitions, and also give some enumeration results.