(a) Show that if $p$ is a prime number and $k \geq 1$ is an integer, then
$$\Phi _ { p ^ { k } } = X ^ { ( p - 1 ) p ^ { k - 1 } } + X ^ { ( p - 2 ) p ^ { k - 1 } } + \cdots + X ^ { p ^ { k - 1 } } + 1$$
(b) Calculate $\Phi _ { n }$ for $n = 1,2,3,4,5,6$.