Classify
∞∑n=31nlog(n)
as absolutely convergent, conditionally convergent or divergent.
Is it,
∞∑n=31n is a divergent p-series as p=1, and
lim by comparison test. And this converges to 0.
So,
\sum_{n=3}^\infty \frac{1}{n\log (n)}
is conditionally convergence?
I'm not sure if I'm doing right or not. Could you guide me?
Thanks in advance! :)
Answer
Note that if your given series is convergent then it's also absolutely convergent since \frac{1}{n\log n}\geq 0\quad \forall n\geq 3.
Now, since the sequence (\frac{1}{n\log n}) is decreasing to 0 so by the integral test your series has the same nature that the improper integral
\int_3^\infty\frac{dx}{x\log x}=\left[\log(\log(x))\right]_3^{\to\infty}=\infty
hence the series is divergent.
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