It's known that the seventh coefficient of $\Phi_{105}(x)$ is -2 and that's the first occurrence of a coefficient with absolute value greater than 1 for a cyclotomic polynomial. When I did a quick check for the seventh coefficient of $\Phi_{n}(x)$ where $n=105k$ with gcd$(105,k)=1$ and $\mu(k)\neq 0$ they all came out to be greater than 1 in absolute value. Is it true in general or there is a counterexample to this?