Let $!$ be the D6: Natural number factorial function.
The Napier's constant is the D993: Real number \begin{equation} e : = \frac{1}{1} + \frac{1}{1} + \frac{1}{1 \cdot 2} + \frac{1}{1 \cdot 2 \cdot 3} + \frac{1}{1 \cdot 2 \cdot 3 \cdot 4} + \cdots \end{equation}