I added the prime factorization section (needed for Prime Number Theorem and Bertrand postulate). I'm not sure the counting principle I referred to as the Lebesgue counting principle is not really known under some other name. If you happen to know the correct name for it, please, change the corresponding line.
Good new section. I cut the Lebesgue counting bit (and the summation) and described in simpler terms where the sum comes from (though I think my explanation can be improved). If a reader doesn't know this prime factorization information, they'll never understand that summation. (In other words, the tool used to produce the sum was more advanced than the fact the sum represents, making it hard for a new student to follow.) The section's a nice addition. --Rrusczyk 09:48, 3 July 2006 (EDT)