Bulletin of the
Korean Mathematical Society BKMS

An idempotent $e$ of a ring $R$ is called {\it right} (resp., {\it left}) {\it semicentral} if $er=ere$ (resp., $re =ere$) for any $r\in R$, and an idempotent $e$ of $R\backslash \{0,1\}$ will be called {\it right} (resp., {\it left}) {\it quasicentral} provided that for any $r\in R$, there exists an idempotent $f=f(e,r)\in R\backslash \{0,1\}$ such that $er=erf$ (resp., $re=fre$). We show the whole shapes of idempotents and right (left) semicentral idempotents of upper triangular matrix rings and polynomial rings. We next prove that every nontrivial idempotent of the $n$ by $n$ full matrix ring over a principal ideal domain is right and left quasicentral and, applying this result, we can find many right (left) quasicentral idempotents but not right (left) semicentral.

Keywords: Idempotent, right (left) semicentral idempotent, right (left) quasicentral idempotent, right (left) quasi-Abelian ring, matrix ring, polynomial ring

MSC numbers: Primary 16S50, 16U40

Supported by: The fourth named author was supported by the Science and Technology Research Project of Education Department of Jilin Province, China(JJKH20210563KJ).