If $$\omega$$ is an imaginary cube root of unity, then the value of (2 $$-$$ $$\omega$$) (2 $$-$$ $$\omega$$²) + 2(3 $$-$$ $$\omega$$)(3 $$-$$ $$\omega$$²) + ... + (n $$-$$ 1) (n $$-$$ $$\omega$$)(n $$-$$ $$\omega$$²) is