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((-1)^(n+1)/(n!(n+0.5)))(2^(-n-0.5)-1)

Sum of series ((-1)^(n+1)/(n!(n+0.5)))(2^(-n-0.5)-1)



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The solution

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  oo                              
____                              
\   `                             
 \         n + 1                  
  \    (-1)        / -n - 1/2    \
  /   ------------*\2         - 1/
 /    n!*(n + 1/2)                
/___,                             
n = 0                             
$$\sum_{n=0}^{\infty} \frac{\left(-1\right)^{n + 1}}{\left(n + \frac{1}{2}\right) n!} \left(2^{- n - \frac{1}{2}} - 1\right)$$
Sum(((-1)^(n + 1)/((factorial(n)*(n + 1/2))))*(2^(-n - 1/2) - 1), (n, 0, oo))
The radius of convergence of the power series
Given number:
$$\frac{\left(-1\right)^{n + 1}}{\left(n + \frac{1}{2}\right) n!} \left(2^{- n - \frac{1}{2}} - 1\right)$$
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
$$a_{n} = \frac{\left(-1\right)^{n + 1} \left(2^{- n - \frac{1}{2}} - 1\right)}{\left(n + \frac{1}{2}\right) n!}$$
and
$$x_{0} = 0$$
,
$$d = 0$$
,
$$c = 1$$
then
$$1 = \lim_{n \to \infty}\left(\frac{\left(n + \frac{3}{2}\right) \left|{\frac{\left(1 - 2^{- (n + \frac{1}{2})}\right) \left(n + 1\right)!}{\left(1 - 2^{- (n + \frac{3}{2})}\right) n!}}\right|}{n + \frac{1}{2}}\right)$$
Let's take the limit
we find
False

False
The rate of convergence of the power series
The answer [src]
                          /  ___\
  ____            ____    |\/ 2 |
\/ pi *erf(1) - \/ pi *erf|-----|
                          \  2  /
$$- \sqrt{\pi} \operatorname{erf}{\left(\frac{\sqrt{2}}{2} \right)} + \sqrt{\pi} \operatorname{erf}{\left(1 \right)}$$
sqrt(pi)*erf(1) - sqrt(pi)*erf(sqrt(2)/2)
Numerical answer [src]
0.283612646313745147780262346225
0.283612646313745147780262346225
The graph
Sum of series ((-1)^(n+1)/(n!(n+0.5)))(2^(-n-0.5)-1)

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