f(x) = (x^3 + x^6 + \ldots + x^{30})(x + x^4 + \ldots + \x^{28})(x^2 + x^5 + \ldots x^{29}) \\ \\
=x^6 (1 + x^3 + \ldots + x^{27})^3 \\ \\ =x^6\left(\displaystyle\frac{1-x^{30}}{1-x^3}\right)^3