Among the given elements: - Eu (Europium), Er (Erbium), Tb (Terbium), Yb (Ytterbium), and Lu (Lutetium) all belong to the lanthanoid series. Cm (Curium) belongs to the actinide series.
Hence, the number of elements that do not belong to lanthanoids is 1 (Cm).
Let \( S = \left\{ m \in \mathbb{Z} : A^m + A^m = 3I - A^{-6} \right\} \), where
\[ A = \begin{bmatrix} 2 & -1 \\ 1 & 0 \end{bmatrix} \]Then \( n(S) \) is equal to ______.