Let $\mathbb{B} = \{ 0, 1 \}$ be the D217: Set of boolean numbers.
Let $N \in \{ 1, 2, 3, \ldots \}$ be a D5094: Positive integer.

Then \begin{equation} \# \left\{ f \mid f : \mathbb{B}^N \to \mathbb{B} \right\} = 2^{2^N} \end{equation}