Find all complex numbers such that the series

converges.

We consider the limit of the th root of the terms of the series,

Hence, the series converges if and only if .

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Stumbling Robot

A Fraction of a Dot
#
Find all *z* such that the series *n*^{n}z^{n} converges

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2 comments

### Point out an error, ask a question, offer an alternative solution (to use Latex type [latexpage] at the top of your comment):

Find all complex numbers such that the series

converges.

We consider the limit of the th root of the terms of the series,

Hence, the series converges if and only if .

Is it the root test used here? I do not think that is legal, since the root test is defined only for real numbers in Apostol (it requires a sequence of non-negative terms, which nz clearly does not follow).

Hello!

Yes, I think it’s a mistake too, as an alternative it can be proved that except when the necessary condition of convergence is not satisfied.

When z=0, if we want to be pedantic, we can show that the limit of partial sums is as goes to .

Cheers!