Norm of the discrete Cesàaro operator minus identity

The norm of $C-I$ on $\ell^p$, where $C$ is the Ces\`aro operator, shown to be $1/(p-1)$ when $1<p\le2$. This verifies a recent conjecture G. J. O. Jameson. $\ell^p$ also determined $2< p<\infty$. two parts together answer question raised by Bennett in 1996. Operator norms continuous case, Hardy's averaging operator minus identity, are already known. Norms discrete and cases coincide.