A new infinite family of $\sigma$-elementary rings

A cover of an associative (not necessarily commutative nor unital) ring $R$ is a collection of proper subrings of $R$ whose set-theoretic union equals $R$. If such a cover exists, then the covering number $\sigma (R)$ of $R$ is the cardinality of a minimal cover, and a ring $R$ is called $\sigma$-elementary if $\sigma (R)<\sigma (R\mathrm{/}I)$ for every nonzero two-sided ideal $I$ of $R$. In this paper, we provide the first examples of $\sigma$-elementary rings $R$ that have nontrivial Jacobson radical $J$ with $R\mathrm{/}J$ noncommutative, and we determine the covering numbers of these rings.