Understanding a statement about the series S=\sum_{2}^{\infty}\frac{1}{n\ln n}

Ben Shaver

Ben Shaver

Answered question

2022-01-13

Understanding a statement about the series
S=21nlnn

Answer & Explanation

sukljama2

sukljama2

Beginner2022-01-14Added 32 answers

Step 1
By nlnn<n1+ϵ,
thus
1nlnn>1n1+ϵ
The series
1n1+ϵ
converges. This cannot be conclusive about the convergence of S, because S is bigger than something finite then we don't know if S is finite or infinite. Hence, you should use integral.
Corgnatiui

Corgnatiui

Beginner2022-01-15Added 35 answers

Step 1
To avoid all confusions and sticking to explanations using words like faster and slower which reduce the rigour of the argument you should directly look into the Integral Test or the Cauchy Condensation test.
By Cauchy Condensation test it suffices to check convergence of the series
2n2nnln(2)=1nln(2)
which diverges as 1n is divergent.

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