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(1/n)arctg(1/(n^(1/2)))

Sum of series (1/n)arctg(1/(n^(1/2)))



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The solution

You have entered [src]
  oo              
_____             
\    `            
 \         /  1  \
  \    atan|-----|
   \       |  ___|
   /       \\/ n /
  /    -----------
 /          n     
/____,            
n = 1             
$$\sum_{n=1}^{\infty} \frac{\operatorname{atan}{\left(\frac{1}{\sqrt{n}} \right)}}{n}$$
Sum(atan(1/(sqrt(n)))/n, (n, 1, oo))
The radius of convergence of the power series
Given number:
$$\frac{\operatorname{atan}{\left(\frac{1}{\sqrt{n}} \right)}}{n}$$
It is a series of species
$$a_{n} \left(c x - x_{0}\right)^{d n}$$
- power series.
The radius of convergence of a power series can be calculated by the formula:
$$R^{d} = \frac{x_{0} + \lim_{n \to \infty} \left|{\frac{a_{n}}{a_{n + 1}}}\right|}{c}$$
In this case
$$a_{n} = \frac{\operatorname{atan}{\left(\frac{1}{\sqrt{n}} \right)}}{n}$$
and
$$x_{0} = 0$$
,
$$d = 0$$
,
$$c = 1$$
then
$$1 = \lim_{n \to \infty}\left(\frac{\left(n + 1\right) \operatorname{atan}{\left(\frac{1}{\sqrt{n}} \right)}}{n \operatorname{atan}{\left(\frac{1}{\sqrt{n + 1}} \right)}}\right)$$
Let's take the limit
we find
True

False
The rate of convergence of the power series
The answer [src]
  oo              
_____             
\    `            
 \         /  1  \
  \    atan|-----|
   \       |  ___|
   /       \\/ n /
  /    -----------
 /          n     
/____,            
n = 1             
$$\sum_{n=1}^{\infty} \frac{\operatorname{atan}{\left(\frac{1}{\sqrt{n}} \right)}}{n}$$
Sum(atan(1/sqrt(n))/n, (n, 1, oo))
Numerical answer [src]
2.30350012572748872060340509734
2.30350012572748872060340509734
The graph
Sum of series (1/n)arctg(1/(n^(1/2)))

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