A conjecture on hyponormality for the Ces\`aro matrix of positive integer order

Abstract

It is already known that the Ces\`{a}ro matrices of orders one and two are coposinormal, hyponormal operators on $\ell^2$. Here it is shown that the Ces\`{a}ro matrices of order three and four are also coposinormal, hyponormal; the proofs employ posinormality, achieved by means of a diagonal interrupter, and elementary computational techniques from calculus. A conjecture is then propounded for the Ces\`{a}ro matrix of positive integer order greater than four.