The
Collatz function is the
D4949: Natural number function
\begin{equation}
\{ 1, 2, 3, \ldots \} \to \{ 1, 2, 3, \ldots \}, \quad
n \mapsto
\begin{cases}
3 n + 1, \quad & n \in \{ 1, 3, 5, \ldots \} \\
n / 2, \quad & n \in \{ 0, 2, 4, \ldots \}
\end{cases}
\end{equation}
