The
Möbius function is the
D4948: Integer function
\begin{equation}
\mathbb{N} \to \{ -1, 0, 1 \}, \quad
n \mapsto
\begin{cases}
(-1)^m, \quad & n \text{ equals a product of } m \text{ distinct prime integers} \\
0, \quad & \text{otherwise}
\end{cases}
\end{equation}
