The slow crawl

Calculus Level 4

n = 3 1 n ln ( n ) ln ( ln ( n ) ) \large \sum\limits_{n=3}^{\infty} \dfrac{1}{n\ln(n) \ln(\ln(n))}

Does the above series converge?

Yes No Unknowable

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2 solutions

Abhishek Sinha
Jan 28, 2016

n = 3 1 n ln ( n ) ln ( ln ( n ) ) 3 1 x ln ( x ) ln ( ln ( x ) ) d x = [ ln ( ln ( ln ( x ) ) ) ] 3 = \sum_{n=3}^{\infty}\frac{1}{n \ln(n) \ln(\ln(n))} \geq \int_{3}^{\infty}\frac{1}{x \ln(x) \ln(\ln(x))} dx = [\ln(\ln (\ln (x)))]_{3}^{\infty}=\infty Hence the series diverges.

Please explain!

Rishi Raj - 5 years, 3 months ago

How is your supposition true?

Srikeshav Kothapalli - 5 years, 4 months ago

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Can you please elaborate on your question ?

Abhishek Sinha - 5 years, 4 months ago

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Is the inequality true because the function is decreasing?

Srikeshav Kothapalli - 5 years, 4 months ago

https://en.wikipedia.org/wiki/Cauchy condensation test
See this for more info about the cauchy condensation test And watch this video for more info about the limit comparison test : - https://www.youtube.com/watch?v=19bXWl9mqho

In the second and last step it should be ln(ln(2)) instead of ln2. Sorry for the mistake...

Arghyadeep Chatterjee - 2 years, 1 month ago

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