On the coefficients of divisors of $x^n-1$

Let $a(r,n)$ be $r$th coefficient of $n$th cyclotomic polynomial. Suzuki proved that $\{a(r,n)\mathrm{\mid }r\ge 1,n\ge 1\}=\mathbb{Z}$. If $m$ and $n$ are two natural numbers we prove an analogue of Suzuki’s theorem for divisors of $x^n-1$ with exactly $m$ irreducible factors. We prove that for every finite sequence of integers $n_1,\dots ,n_r$ there exists a divisor $f(x)={\sum }_{i=0}^{deg(f)}{c}_i{x}^i$ of $x^n-1$ for some $n\in \mathbb{N}$ such that $c_i=n_i$ for $1\le i\le r$. Let $H(r,n)$ denote the maximum absolute value of $r$th coefficient of divisors of $x^n-1$. In the last section of the paper we give tight bounds for $H(r,n)$.