Weierstrass Product Theorem

Theorem
Let $\left\langle{a_k}\right\rangle$ be a sequence of non-zero complex numbers such that:
 * $\left\vert{a_n}\right\vert \to \infty$ as $n \to \infty$

Let $\left\langle{p_n}\right\rangle$ be a sequence of non-negative integers for which the series:
 * $\displaystyle \sum_{n \mathop = 1}^\infty \left({\dfrac r {\left\vert{a_n}\right\vert} }\right)^{1 + p_n}$

converges for every $r \in \R_{> 0}$.

The function:


 * $\displaystyle f \left({z}\right) = \prod_{n \mathop = 1}^\infty E_{p_n} \left({\frac z {a_n} }\right)$

is entire with zeros only at points $a_n$ where $E_{p_n}$ are Weierstrass elementary factors.

Proof
Use Infinite Product of Analytic Functions.

Also see

 * Weierstrass Factorization Theorem