Limit of the Euler totient function

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    Euler Function Limit
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Discussion Overview

The discussion revolves around the limit of the Euler totient function, particularly whether it can be expressed in terms of the product over prime numbers as \( n \) approaches infinity. Participants explore the behavior of the function and its discontinuities, questioning the validity of taking limits in this context.

Discussion Character

  • Exploratory
  • Mathematical reasoning
  • Debate/contested

Main Points Raised

  • One participant proposes that the limit of the Euler totient function can be expressed as \( \lim_{n \rightarrow \infty}(\varphi(n))=\lim_{n \rightarrow \infty}(n) \cdot \prod_{i=1}^{\infty}(1-\frac{1}{p_i}) \), suggesting that the function tends to infinity despite potential discontinuities.
  • Another participant agrees with the initial formula and discusses the relationship between the number of prime factors of \( n \) and the behavior of \( \varphi(n) \), noting that while the number of prime factors generally increases, it is not strictly true for all individual numbers.
  • A different participant raises a concern about the ability to take limits when certain numbers are 'discontinuous' from the general trend, implying that such discontinuities could affect the validity of the limit.
  • One participant uses an analogy involving a piecewise function to illustrate the concept of limits and continuity, questioning the interpretation of discontinuities in the context of the Euler totient function.
  • Another participant expresses gratitude for the clarification provided by the analogy, indicating a lack of formal experience with limits.

Areas of Agreement / Disagreement

Participants express differing views on the implications of discontinuities for taking limits, with some supporting the proposed formula while others question its validity based on the behavior of specific numbers. The discussion remains unresolved regarding the overall applicability of the limit in this context.

Contextual Notes

Participants highlight the potential discontinuities in the Euler totient function and the implications of these for taking limits, but do not reach a consensus on how these factors influence the proposed limit expression.

henpen
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My question is relatively breif: is it true that

\displaystyle \lim_{n \rightarrow \infty}(\varphi(n))=\lim_{n \rightarrow \infty}(n) \cdot \prod_{i=1}^{\infty}(1-\frac{1}{p_i})
Where p is prime? Pehaps \varphi(n) is too discontinuous to take the limit of, but it would seem that as it increases to infinity the function should tend to infinity, with fewer anomalies.

If this were true,

\displaystyle \zeta(1)=\frac{1}{ \prod_{i=1}^{\infty}(1-\frac{1}{p_i})}=\frac{1}{\lim_{n \rightarrow \infty}(\frac{\varphi(n)}{n})}=\lim_{n \rightarrow \infty}(\frac{n}{\varphi(n)})
 
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henpen said:
My question is relatively brief: is it true that

\displaystyle \lim_{n \rightarrow \infty}(\varphi(n))=\lim_{n \rightarrow \infty}(n) \cdot \prod_{i=1}^{\infty}(1-\frac{1}{p_i})
Where p is prime? Pehaps \varphi(n) is too discontinuous to take the limit of, but it would seem that as it increases to infinity the function should tend to infinity, with fewer anomalies.

If this were true,

\displaystyle \zeta(1)=\frac{1}{ \prod_{i=1}^{\infty}(1-\frac{1}{p_i})}=\frac{1}{\lim_{n \rightarrow \infty}(\frac{\varphi(n)}{n})}=\lim_{n \rightarrow \infty}(\frac{n}{\varphi(n)})
Let ##\mathfrak{P}_n## be the set of all distinct prime divisors of a number n.
Consider that ##\displaystyle \varphi(n) = n \prod_{i=1}^{\sharp\mathfrak{P}_n}\left[1-\frac{1}{p_i}\right]##, where ##\sharp\mathfrak{P}_n## is the cardinality of ##\mathfrak{P}_n## and ##p_i## is the ith element of ##\mathfrak{P}_n##. As n increases, its number of prime factors tends to increase, but this trend is in no way strictly true for individual numbers. An example of a relatively large number that does not have a large number of prime factors is 87178291199, which has only one prime factor. :-p

Thus, using basic properties of limits, your formula should be correct.
 
The problem I has was that if particular numbers are 'discontinuous' from the general trend, you can't take the limit, even if the general trend tends to infinity.
 
henpen said:
The problem I has was that if particular numbers are 'discontinuous' from the general trend, you can't take the limit, even if the general trend tends to infinity.
Consider a function ##f: \mathbb{R}\rightarrow\mathbb{R}\cup\left\{Tootsiepop\right\}##, where, for ##x\in\mathbb{R}##, ##f(x)=\left\{\begin{array} , x , x\neq2 \\ Tootsiepop , x=2 \end{array}\right.##

As x approaches 2, f(x) approaches 2. However, f(2)=Tootsiepop.

This is not a continuous function, but the limit as x approaches 2 is defined. So, I don't understand what you mean...
 
The example cleared up a lot, thanks. I've little formal experience with limits.
 

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