Show that a CCD is rotatable when $alpha=left(n_{F} ight)^{1 / 4}$ where $n_{F}$ is the number of points used in the factorial portion of the

Show that a CCD is rotatable when $\alpha=\left(n_{F}\right)^{1 / 4}$ where $n_{F}$ is the number of points used in the factorial portion of the design.