It is already known that the Cesàro matrices of orders one and two are coposinormal, hyponormal operators on ℓ 2 . Here it is shown that the Cesàro 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 Cesàro matrix of positive integer order greater than four.
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