In the context of finite projective planes I am interested in the Diophantine equation $\frac{x^3-1}{x-1} = y^z$, which is also written as $x^2 + x + 1 = y^z$, for $z>1$. I stumbled by accident on the case $x=18$, $y=7$, $z=3$. Does anyone know more about integer solutions to this equation?