Polynomial analogue of the Kempner function
Xiumei Li, Min Sha · arXiv (Cornell University) · 2019
In the integer case, the Kempner function of a positive integer $n$ is defined to be the smallest positive integer $k$ such that $n$ divides the factorial $k!$. In this paper, we first define a natural order for polynomials in $\F_q[t]$ over a finite field $\F_q$ and then define the Kempner function of a non-zero polynomial $f \in \F_q[t]$, denoted by $K(f)$, to be the smallest polynomial $g$ such that $f$ divides the Carlitz factorial of $g$. In particular, we establish an analogue of a problem of Erd{\H o}s, which implies that for almost all polynomials $f$, $K(f)=t^d$, where $d$ is the maximal degree of the irreducible factors of $f$.