An example of a series that diverges and exhibits no pattern?

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Discussion Overview

The discussion revolves around identifying examples of series that diverge and exhibit no discernible pattern. Participants explore various series and their characteristics, particularly in the context of divergence and the absence of recognizable behavior.

Discussion Character

  • Exploratory, Technical explanation, Debate/contested

Main Points Raised

  • One participant requests examples of series that diverge without exhibiting a pattern, noting that their course only covers certain types of divergence.
  • Another participant suggests defining the terms of the series as the decimal digits of ##\pi##, proposing that the series $$\sum_{n=1}^{\infty}a_n$$ diverges while $$\sum_{n=1}^{\infty}\frac{a_n}{n^2}$$ converges.
  • A participant expresses surprise at the example provided, indicating that they had not considered it in that context before.
  • Another participant proposes the series $$\sum_{i=1}^\infty \frac{1}{p_n}$$, where ##p_n## is the nth prime number, suggesting that this series also diverges.
  • A later reply mentions Liouville numbers as a universal example of a series that diverges without a pattern.

Areas of Agreement / Disagreement

Participants present multiple examples of divergent series, but there is no consensus on a single definitive example or characteristic that universally applies to all series exhibiting no pattern.

Contextual Notes

Some participants express uncertainty about the definitions and characteristics of the series discussed, particularly in relation to their coursework and the examples provided.

Permanence
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Hi I was hoping someone could provide me with a couple examples of series that exhibit no pattern. In my course we only cover divergence that involves the limit tending to infinity or oscillation. My textbook informs me that in some rare cases no pattern may be exhibited, but doesn't list any examples. I'm drawing a blank on brainstorming.

Thanks!

PS
Also are there any specific characteristics or tests that would clue me into knowing that it exhibits no patterns.
 
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How about if you define ##a_n## to be the ##n##'th decimal digit of ##\pi##?

Then this series diverges:
$$\sum_{n=1}^{\infty}a_n$$
because the terms do not converge to zero, and this series converges
$$\sum_{n=1}^{\infty}\frac{a_n}{n^2}$$
by comparison with ##\sum 10/n^2##.
 
Gah I feel so stupid. I've seen that specific example before, but I never really thought about it that way. In our class we've always defined a(sub)n to be a particular function that we've seen before.

Thank you Jbunniii for the swift response!
 
How about:
[tex]\sum_{i=1}^\infty \frac{1}{p_n}[/tex]
where p_n is the nth prime number? I think this also diverges.
 
Permanence said:
Gah I feel so stupid. I've seen that specific example before, but I never really thought about it that way. In our class we've always defined a(sub)n to be a particular function that we've seen before.

Thank you Jbunniii for the swift response!

For education a Liouville number is the universal example of such a series.

http://en.wikipedia.org/wiki/Liouville_number
 

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