If you factor $x^n-1\in\mathbb{Q}[x]$, then for $n\leq 104$ the coefficients of the factors are in $\{-1, 0, 1\}$. (This is not true for $n=105$, however). Let $U$ be the set of positive integers $n$ such that all the coefficients of the irreducible factors of $x^n-1$ over $\mathbb{Q}$ are either $-1$, $0$, or $1$.

For $A\subseteq \mathbb{N}$ set $\mu(A) = \lim\inf_{n\to\infty}\frac{|A\cap\{1,\ldots,n\}|}{n}$.

What is the value of $\mu(U)$?