I've been working on this homework exercise for quite some time now and I just won't succeed. Any help would be appreciated.
Let ω(n) be the number of distinct prime divisors of n. I need to prove that ω(n)=O(log(n)loglog(n)) as x→∞. There is a hint which says to first prove ω(n)!≤n (which was easy) . Furthermore, I may use ω(n)!≥exp(ω(n)log(ω(n))−ω(n)).
From these hints it follows that ω(n)log(ω(n))−ω(n)≤log(n) and thus ω(n)≤log(n)/(log(ω(n))−1), but then I get stuck.
Alternatively, ω(n)log(ω(n))≤log(n)+ω(n)≤2log(n) and I get stuck again.
I've found a proof which I understand but it does not use any of the hints. Since I have been giving this some time now, I would really like to know how to do it in the way suggested by the exercise.
Thanks in advance!
Answer
Once you have the inequality ω(n)logω(n)≤2logn you're basically there. Now assume for contradiction that for all large enough n we have ω(n)>Clognloglogn. Here C is some large constant, though actually C>2 suffices.
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