Sequences ${a_k}$ and ${c_k}$ such that $a_k$, $c_k \rightarrow 0$, $\sum_k a_k = \infty$, and $\sum_k\left(\frac{a_k}{c_k}\right )^{2} < \infty $

Question

Is there an example of two sequences for which the following conditions hold?

Sequences ${a_k}$ and ${c_k}$ such that $a_k$, $c_k \rightarrow 0$, $\sum_k a_k = \infty$, and $\sum_k\left(\frac{a_k}{c_k}\right )^{2} < \infty $