- ECM
  See "An Implementation of the Elliptic Curve Integer Factorization Method"
  by Bosma and AK Lenstra
  Also http://www.ne.lpfritz.org/ftp/Prime/

- ECM should add a stage 2.

- prime_count - needs the pc(#) option as well as pc(#,#)

- Consider adding Lehmer's method for prime count.  The only use I can really
  think of would be 32-bit machines.  I worry that the overhead of GMP would
  kill us, and some method using __uint64s, or even Math::Int64 would be
  faster.

- nth_prime

- GMP SQUFOF could use a better implementation, though low priority since it
  just isn't going to be the right algorithm for numbers > 2^64.  Mainly what
  it needs is to pay attention to the rounds argument.  Perhaps race.

- Add Riemann R function