Infinite alternating series with repeated logarithms

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Homework Help Overview

The discussion revolves around the convergence and evaluation of an infinite alternating series involving repeated logarithmic functions, specifically the series \(\sum_{i=2}^{\infty}(-1)^i \cdot \lg^{(i)} n\), where \(n\) is a natural number.

Discussion Character

  • Exploratory, Assumption checking, Conceptual clarification

Approaches and Questions Raised

  • Participants discuss the convergence of the series, with one participant mentioning the use of the Leibniz test. Others raise concerns about the series being well-defined and question the behavior of the logarithmic terms as \(i\) increases.

Discussion Status

The discussion has highlighted differing views on the convergence and definition of the series. While some participants express interest in numerical estimates, others point out potential issues with the series' definition, leading to a cancellation of the question by one participant. The conversation remains open-ended without a clear resolution.

Contextual Notes

There are indications that the series may not be well-defined for certain values of \(n\), and participants are grappling with the implications of this on the convergence and evaluation of the series.

LeifEricson
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Homework Statement



Calculate the sum of the following series:
[tex]\sum_{i=2}^{\infty}(-1)^i \cdot \lg ^{(i)} n[/tex]

Where (i) as a super-script signifies number of times lg was operated i.e. [tex]\lg ^{(3)} n = (\lg (\lg (\lg n)))[/tex], and n is a natural number.

Homework Equations





The Attempt at a Solution



I proved by Leibniz test that this series converges. But I don't know how to find the number to which it converges to.

Thanks.
 
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I really don't know how to help you... but since you know it converges you can use the numerical estimate to see if it looks like any famous number?

I hope someone helps I'm really interested in this!
 
If you try doing a numerical estimate it will blow up. Which is informative. Eventually ln^(k)(n)<1. Then ln^(k+1)(n)<0. Now what's ln^(k+2)(n)?? The series isn't even well defined much less convergent.
 
You are right.
The series isn't well defined so I cancel this question. I apologize.
 
Oh that makes me feel a little better. I could not even see how you had it converging.

:-p
 
LeifEricson said:
You are right.
The series isn't well defined so I cancel this question. I apologize.

No need for apologies! It's a perfectly valid question. It makes a good 'think about it' exercise. It does look at first glance like it ought to be a good candidate for an alternating series test.
 
Last edited:

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