Sum of Reciprocals of Powers as Euler Product/Proof 2

Proof
From Sum of Geometric Progression:
 * $\dfrac 1 {1 - p^{-z} } = 1 + \dfrac 1 {p^z} + \dfrac 1 {p^{2 z} } + \cdots$

From Sum of Reciprocals of Powers is Absolutely Convergent iff Modulus of Power is Greater than One:
 * $\displaystyle \sum_{n \mathop \ge 1} n^{-z}$ is absolutely convergent


 * $\left\lvert{z}\right\rvert \ge 1$
 * $\left\lvert{z}\right\rvert \ge 1$

Thus:

The result follows from the Fundamental Theorem of Arithmetic.