Out of curiosity, I looked at perllocal.pod. It looks like Math::MPFR installed automatically during the Math::Prime::Util cpan installation.

$ vi /opt/perl-5.26.1/lib/5.26.1/darwin-thread-multi-2level/perllocal.
+pod

Math::Prime::Util::GMP
Math::Prime::Util
-- auto-installed Math::MPFR
-- auto-installed Math::BigInt::GMP
[download]

Regarding use integer (thanks haukex), the spigot Perl code ran 1.36 times faster on my Mac. Math::Prime::Util is already incredibly fast. Now wonder in amazement on what you will do next.