Function: ispseudoprimepower
Section: number_theoretical
C-Name: ispseudoprimepower
Prototype: lGD&
Help: ispseudoprimepower(x,{&n}): if x = p^k is a pseudo-prime power (p
 pseudo-prime, k > 0),
 return k, else return 0. If n is present, and the function returns a non-zero
 result, set n to p, the k-th root of x.
Doc: if $x = p^k$ is a pseudo-prime power ($p$ pseudo-prime as per
 \tet{ispseudoprime}, $k > 0$), return $k$, else
 return 0. If a second argument $\&n$ is given and $x$ is indeed
 the $k$-th power of a prime $p$, sets $n$ to $p$.

 More precisely, $k$ is always the largest integer such that $x = n^k$ for
 some integer $n$ and, when $n \leq  2^{64}$ the function returns $k > 0$ if and
 only if $n$ is indeed prime. When $n > 2^{64}$ is larger than the threshold,
 the function may return $1$ even though $n$ is composite: it only passed
 an \kbd{ispseudoprime(n)} test.
