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Sum of series (-1)^n(x^(14n)/n!)



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The solution

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  oo             
____             
\   `            
 \           14*n
  \       n x    
  /   (-1) *-----
 /            n! 
/___,            
n = 1            
$$\sum_{n=1}^{\infty} \left(-1\right)^{n} \frac{x^{14 n}}{n!}$$
Sum((-1)^n*(x^(14*n)/factorial(n)), (n, 1, oo))
The radius of convergence of the power series
Given number:
$$\left(-1\right)^{n} \frac{x^{14 n}}{n!}$$
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
$$a_{n} = \frac{\left(-1\right)^{n}}{n!}$$
and
$$x_{0} = 0$$
,
$$d = 14$$
,
$$c = 1$$
then
$$R^{14} = \lim_{n \to \infty} \left|{\frac{\left(n + 1\right)!}{n!}}\right|$$
Let's take the limit
we find
$$R^{14} = \infty$$
$$R = \infty$$
The answer [src]
     /         14\
     |       -x  |
  14 | 1    e    |
-x  *|--- - -----|
     | 14     14 |
     \x      x   /
$$- x^{14} \left(\frac{1}{x^{14}} - \frac{e^{- x^{14}}}{x^{14}}\right)$$
-x^14*(x^(-14) - exp(-x^14)/x^14)

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