Apparent indiscrepancy in the average value of phi function

Therefore, the average value of the phi function up to n is approximately ##\frac{3n^2}{\pi^2}##, which is consistent with the statement on page 268 of Introduction to the Theory of Numbers. In summary, the average order of the Totient function is ##\frac{6n}{\pi^2}##, and the average value of the phi function up to n is approximately ##\frac{3n^2}{\pi^2}##.
  • #1
Whovian
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So, while solving a problem a friend came up with involving the Totient function, I ended up doing a bit of research into the average asymptotics of the function. On page 268 of Introduction to the Theory of Numbers, it's mentioned that "The average of order of ##\phi\left(n\right)## is ##\frac{6\cdot n}{\pi^2}##. More precisely, ##\Phi\left(n\right)=\phi\left(1\right)+\ldots+\phi\left(n\right)=\frac{3\cdot n^2}{\pi^2}+O\left(n\cdot\log\left(n\right)\right)##."

My question is, wouldn't this mean ##\frac{\phi\left(1\right)+\ldots+\phi\left(n\right)}{n}\approx\frac{3\cdot n}{\pi^2}##, so the average value of the phi function up to n would be approximately ##\frac{3\cdot n}{\pi^2}## and not, as previously stated, ##\frac{6\cdot n}{\pi^2}##?
 
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  • #2
Recall that an arithmetic function ##f## is said to be of the average order of a function ##g## if
$$f(1)+f(2) + \cdots + f(n) \sim g(1) + g(2) + \cdots + g(n)$$
Let ##f(n)=\phi(n)## and ##g(n)=\frac{6n}{\pi^2}##.
Then ##\phi(n)## has average order ##\frac{6n}{\pi^2}## means that
$$\phi(1)+\phi(2)+\cdots+\phi(n)\sim\frac{6}{\pi^2}(1+2+\cdots+n)$$
and ##1+2+\cdots+n\sim\frac{1}{2}n^2##.
 
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Related to Apparent indiscrepancy in the average value of phi function

1. What is the phi function and why is its average value important?

The phi function, also known as Euler's totient function, is a mathematical function that counts the number of positive integers less than or equal to a given number that are relatively prime to that number. The average value of the phi function is important because it is used in various mathematical equations and has applications in number theory and cryptography.

2. What is the apparent discrepancy in the average value of the phi function?

The apparent discrepancy in the average value of the phi function refers to the fact that the average value of the function is often not an integer, even though it is counting the number of positive integers. This can be confusing for some and may seem like a discrepancy at first glance.

3. How is the average value of the phi function calculated?

The average value of the phi function for a given number, n, is calculated by taking the sum of the phi values for all numbers less than or equal to n and dividing it by n. This is represented by the equation: Average value = (sum of phi values for numbers less than or equal to n) / n.

4. Why is there a discrepancy in the average value of the phi function?

The discrepancy in the average value of the phi function is due to the fact that the function is not a linear function. This means that as the input number increases, the average value of the function does not increase at a constant rate. This can lead to non-integer values for the average.

5. Are there any real-world implications for the apparent discrepancy in the average value of the phi function?

While the apparent discrepancy in the average value of the phi function may seem confusing, it does not have any significant real-world implications. It is simply a result of the mathematical properties of the function and does not affect its applications or usefulness in various fields of study.

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