\begin{definition}[Definition:Primitive Prime Factor of Fibonacci Number]
Let $F_n$ denote the $n$th Fibonacci number.
A '''primitive prime factor of $F_n$''' is a prime number $p$ of $F_n$ such that:
:$p \divides F_n$
:$\nexists k \in \Z_{>0}: k < n: p \divides F_k$
where $a \divides b$ denotes that $a$ is a divisor of $b$.
That is, a prime factor of $F_n$ but of no smaller Fibonacci numbers.
\end{definition}