Convergence of a logaritmic series

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Homework Help Overview

The problem involves analyzing the convergence of a logarithmic series, specifically the series \(\sum_{n=9}^{\infty}\frac{1}{(\ln(\ln(n)))^{\ln(n)}}\). Participants are discussing the criteria for convergence and exploring comparison tests.

Discussion Character

  • Exploratory, Assumption checking, Mathematical reasoning

Approaches and Questions Raised

  • The original poster attempts to apply the comparison test but struggles to find an appropriate function for comparison. They explore the relationship between logarithmic functions and their growth rates.
  • Some participants suggest considering functions smaller than \(\ln(\ln(n))^{\ln(n)}\) for a valid comparison.
  • One participant proposes rewriting the expression to facilitate comparison and suggests using \(n^{2}\) as a potential comparison function.

Discussion Status

The discussion is ongoing, with participants providing insights and suggestions for approaching the convergence analysis. There is a recognition of the need for a suitable comparison function, and multiple interpretations of the series behavior are being explored.

Contextual Notes

Participants are working under the constraints of homework guidelines, which may limit the use of certain resources or methods. The original poster's attempts indicate a focus on understanding the underlying mathematical principles rather than simply finding a solution.

Rono
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Homework Statement


Analyze the convergence of the following series, describing the criteria used:
\displaystyle\sum_{n=9}^{\infty}\frac{1}{(ln(ln(n)))^{ln(n)}}


Homework Equations


None


The Attempt at a Solution


Wolfram Alpha says it converges due to comparison test, however I can't find to get a proper comparison. My main attempt was starting with \displaystyle ln(n)< n and, starting from there, getting:
(ln(ln(n)))^{ln(n)} < (ln(n))^{ln(n)} < n^{ln(n)} < n^{n}
However, after getting their reciprocal, I manage to prove \frac{1}{n^{n}} converges, but that is inconclusive. Any idea to which function I should start with to get the comparison test right?
 
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If you want to show it converges, then you need to replace \ln(\ln(n))^{\ln(n)} with something that is smaller than it, not larger. That means you need to think of a function which is smaller than ln(n) to replace some of those logs with.

It might help to remember that whenever there's a ln(n) in the exponent, you can do some algebra on it to rewrite your function!
 
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All right, managed to get \displaystyle ln(ln(n))^{ln(n)} = n^{ln(ln(ln(n)))}. Guess using n^{2} as the comparison function would work, right? Because at infinity, n^{ln(ln(ln(n)))} ≈ n^{n}, therefore I would it should converge.
 
I don't think that it looks anything close to nn but I agree that n2 is a good comparison.
 

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