  We prove that a finite set of natural numbers $J$ satisfies that $J\cup\{0\}$
is not Sidon if and only if for any operator $T$, the disjoint hypercyclicity
of $\{T^j:j\in J\}$ implies that $T$ is weakly mixing. As an application we
show the existence of a non weakly mixing operator $T$ such that $T\oplus
T^2\ldots \oplus T^n$ is hypercyclic for every $n$.
