The eigenvalue(s) of the matrix
Let \( \mathbb{N} \) be the set of natural numbers and \( f : \mathbb{N} \to \mathbb{N} \) be defined by
Let \( f^n(x) \) denote the \( n \)-fold composition of \( f(x) \). What is the smallest integer \( n \) such that \( f^n(13) = 1 \)?