Problem seven, plus stream-based prime generation.
Naive problem 3
Problem 4
Oops, forgot a file.
New prime factors function, got rid of icky while loop.
Placeholder for problem 5.
Problem 5.  The LCM thing was kind of a pain.
Problem 6.
Forgot to add problem 6, so here's problem 8 as a bonus.
A bit slow, but problem 10.
Problem 13