On the Operator Equations $A^n=A^{\ast }A$

Abstract

Let $n\in \mathbb{N}$ and let $A$ be a closed linear operator (everywhere bounded or unbounded). In this paper, we study (among others) equations of the type $A^{\ast }A=A^n$ where $n\ge 2$ and see when they yield $A=A^{\ast }$ (or a weaker class of operators). In case $n\ge 3$, we have in fact a new class of operators which could placed right after orthogonal projections and just before normal operators.