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