Convergence of a logaritmic series

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SUMMARY

The series \(\sum_{n=9}^{\infty}\frac{1}{(\ln(\ln(n)))^{\ln(n)}}\) converges as established through the comparison test. The discussion highlights the use of \(n^2\) as a suitable comparison function, given that \((\ln(\ln(n)))^{\ln(n)}\) can be approximated by \(n^{\ln(\ln(\ln(n)))}\) at infinity. The analysis confirms that since \(n^{\ln(\ln(\ln(n)))}\) grows slower than \(n^n\), the series converges. Participants emphasized the importance of identifying a function smaller than \(\ln(n)\) for effective comparison.

PREREQUISITES
  • Understanding of series convergence criteria, specifically the comparison test.
  • Familiarity with logarithmic functions and their properties.
  • Knowledge of asymptotic notation and growth rates of functions.
  • Ability to manipulate and rewrite logarithmic expressions in mathematical analysis.
NEXT STEPS
  • Study the comparison test in detail, focusing on its application in series convergence.
  • Learn about asymptotic analysis and how to determine the growth rates of logarithmic functions.
  • Explore advanced logarithmic identities and their implications in series analysis.
  • Investigate other convergence tests, such as the ratio test and root test, for broader understanding.
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Mathematics students, educators, and anyone involved in advanced calculus or analysis who seeks to deepen their understanding of series convergence and logarithmic functions.

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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