# Greatest prime factor

Define the greatest prime factor function $\mathrm{gpf}\colon \mathbb{Z}^+ \rightarrow \mathbb{Z}^+$ by
$\mathrm{gpf}(n) = \{\mathrm{greatest \hspace{2pt} prime \hspace{2pt} factor \hspace{2pt} of \hspace{2pt}}n\}.$