Interesting number theory problem

This is an interesting problem I ran into last week. I thought I might post it as I have very little clue about how to actually solve it. The proof I turned in concluded with "lots of arm waving... QED" (which actually got a fair amount of credit since no one solved it).

Let o(n) denote the Euler totient function. That is, o(n) is the number of integers relatively prime to n that are less than n.

What is the infimum limit as n approached infinity of o(n)/n ?

I reasoned that it is 0 because if you take the k = p1*p2*...*pm (where the p's are primes to the first power), then o(k)/k = (p1 - 1)*(p2 - 1)*...*(pm - 1)/(p1*p2*...*pm), which looks somewhat like 1*2*3*4...*(n-1)/(2*3*5*...*n) which clearly goes to 0 as n approaches infinity... though most of the terms are missing, so I am not sure.

The other thought was products of n*log(n) [roughly the nth prime], though I was unable to get anywhere with this.

Anyways... an interesting problem... anyone got any ideas on it?

Re: Interesting number theory problem

Quote:

*Originally posted by Zach L. *

**This is an interesting problem I ran into last week. I thought I might post it as I have very little clue about how to actually solve it. The proof I turned in concluded with "lots of arm waving... QED" (which actually got a fair amount of credit since no one solved it).**

Let o(n) denote the Euler totient function. That is, o(n) is the number of integers relatively prime to n that are less than n.

What is the infimum limit as n approached infinity of o(n)/n ?

I reasoned that it is 0 because if you take the k = p1*p2*...*pm (where the p's are primes to the first power), then o(k)/k = (p1 - 1)*(p2 - 1)*...*(pm - 1)/(p1*p2*...*pm), which looks somewhat like 1*2*3*4...*(n-1)/(2*3*5*...*n) which clearly goes to 0 as n approaches infinity... though most of the terms are missing, so I am not sure.

The other thought was products of n*log(n) [roughly the nth prime], though I was unable to get anywhere with this.

Anyways... an interesting problem... anyone got any ideas on it?

It certainly looks interesting, and I'd like to be able to give it more of a "go," but I don't know anything about the Euler totient function, sadly. Could you elaborate on it?

You might also want to post it on artofproblemsolving.com under advanced topics or other problem solving... there are some geniuses there.

Re: Interesting number theory problem

Quote:

*Originally posted by Zach L. *

I reasoned that it is 0 because if you take the k = p1*p2*...*pm (where the p's are primes to the first power), then o(k)/k = (p1 - 1)*(p2 - 1)*...*(pm - 1)/(p1*p2*...*pm), which looks somewhat like 1*2*3*4...*(n-1)/(2*3*5*...*n) which clearly goes to 0 as n approaches infinity... though most of the terms are missing, so I am not sure.

Your resoning here sounds plausible. What makes you unsure?

But 'infinity' is hard to work with, OTOH. I'm not sure one can divide infinity into prime numbers like that, it could just as well be one single infinitely large prime number, then the answer would be 1.