Suma de la serie z^ncosinz^n

/       1                            
|  ------------    for |z*cos(z)| < 1
|  1 - z*cos(z)                      
|                                    
|  oo                                
< ___                                
| \  `                               
|  \    n    n                       
|  /   z *cos (z)      otherwise     
| /__,                               
\n = 0                               

$$\begin{cases} \frac{1}{- z \cos{\left(z \right)} + 1} & \text{for}\: \left|{z \cos{\left(z \right)}}\right| < 1 \\\sum_{n=0}^{\infty} z^{n} \cos^{n}{\left(z \right)} & \text{otherwise} \end{cases}$$

Piecewise((1/(1 - z*cos(z)), Abs(z*cos(z)) < 1), (Sum(z^n*cos(z)^n, (n, 0, oo)), True))