  The p-rough numbers are those numbers all of whose prime factors are greater
than p. These are exactly those numbers left after Eratosthenes sieve has been
advanced from 2 through the prime p. Here we show that for fixed p there is a
line of symmetry for the function $\Phi(x,p)$, and we introduce the function
$\Delta \Phi(x,p)$ which is the difference between $\Phi(x,p)$ and the line of
symmetry. $\Delta \Phi(x,p)$ is periodic and bounded and has a rotational
symmetry.
