On two problems of Carlitz and their generalizations

Abstract

Let $N_q$ be the number of solutions to the equation $$(a_1^{}{x}_1^{m_1}+\cdots +a_n^{}{x}_n^{m_n}{)}^k=b{x}_1^{k_1}\cdots x_n^{k_n}$$ over the finite field ${\mathbb{F}}_q={\mathbb{F}}_{p^s}$. Carlitz found formulas for~$N_q$ when $k_1=\cdots =k_n=m_1=\cdots =m_n=1$, $k=2$, $n=3$ or $4$, $p>2$; and when $m_1=\cdots =m_n=2$, $k=k_1=\cdots =k_n=1$, $n=3$ or $4$, $p>2$. In earlier papers, we studied the above equation with $k_1=\cdots =k_n=1$ and obtained some generalizations of Carlitz's results. Recently, Pan, Zhao and Cao considered the case of arbitrary positive integers $k_1,\dots ,k_n$ and proved the formula $N_q=q^{n-1}+(-1{)}^{n-1}$, provided that $\gcd ({\sum }_{j=1}^n(k_j{m}_1\cdots m_n/m_j)-k{m}_1\cdots m_n,q-1)=1$. In this chapter, we determine $N_q$ explicitly in some other cases.

8 pages, 2 tables