Partial Deranged Bell Numbers and Their Combinatorial Properties

TL;DR

This paper introduces partial deranged Bell numbers, exploring their combinatorial properties, explicit formulas, and relationships with classical sequences, providing new insights into Bell number generalizations and their applications.

Contribution

It defines and analyzes partial deranged Bell numbers, connecting them with existing sequences and deriving new formulas and identities, including their relation to complementary Bell numbers.

Findings

Derived explicit formulas and generating functions.

Established relationships with deranged, Stirling, and ordered Bell numbers.

Presented closed-form expressions involving Bernoulli numbers and binomial coefficients.

Abstract

We introduce a novel generalization of deranged Bell numbers by defining the partial deranged Bell numbers $w_{n,r}$, which count the number of set partitions of $\left[ n\right] $ with exactly $r$ fixed blocks, while the remaining blocks are deranged. This construction provides a unified framework that connects partial derangements, Stirling numbers, and ordered Bell numbers. We investigate their combinatorial properties, including explicit formulas, generating functions, and recurrence relations. Moreover, we demonstrate that these numbers are expressible in terms of classical sequences such as deranged Bell numbers and ordered Bell numbers, and reveal their relationship to complementary Bell numbers, offering insights relevant to Wilf's conjecture. Notably, we derive the identity \[ \tilde{\phi}_{n}=\Tilde{w}_{n,0}-\Tilde{w}_{n,1}=\tilde{w}_{n-1,0}-2\tilde {w}_{n-1,2}, \] which illustrates their structural connection to complementary Bell numbers. We also introduce a polynomial expansion for these numbers and explore their connections with exponential polynomials, geometric polynomials, and Bernoulli numbers. These relationships facilitate the derivation of closed-form expressions for certain finite summations involving Stirling numbers of the second kind, Bernoulli numbers, and binomial coefficients, articulated through partial derangement numbers.