Published online by Cambridge University Press: 28 March 2019
A cyclotomic polynomial $\unicode[STIX]{x1D6F7}_{k}(x)$ is an essential cyclotomic factor of
$f(x)\in \mathbb{Z}[x]$ if
$\unicode[STIX]{x1D6F7}_{k}(x)\mid f(x)$ and every prime divisor of
$k$ is less than or equal to the number of terms of
$f.$ We show that if a monic polynomial with coefficients from
$\{-1,0,1\}$ has a cyclotomic factor, then it has an essential cyclotomic factor. We use this result to prove a conjecture posed by Mercer [‘Newman polynomials, reducibility, and roots on the unit circle’, Integers12(4) (2012), 503–519].