Euler's Product form of Riemann Zeta Function

Theorem
Let $s \in \R: s > 1$.

Then:
 * $\displaystyle \sum_{k \mathop \in \N_{>0} } \dfrac 1 {k^s} = \prod_{p \mathop \in \Bbb P} \dfrac 1 {1 - 1 / p^s}$

where $\Bbb P$ denotes the set of all prime numbers.