/ / ___ ___\
| ___ |\/ 3 *\/ x |
|\/ 3 *atanh|-----------|
| \ 3 /
|------------------------ for And(x >= -3, x < 3)
| ___
| \/ x
|
< oo
| ____
| \ `
| \ -n n
| \ 3 *x
| / ------- otherwise
| / 1 + 2*n
| /___,
\ n = 0
$$\begin{cases} \frac{\sqrt{3} \operatorname{atanh}{\left(\frac{\sqrt{3} \sqrt{x}}{3} \right)}}{\sqrt{x}} & \text{for}\: x \geq -3 \wedge x < 3 \\\sum_{n=0}^{\infty} \frac{3^{- n} x^{n}}{2 n + 1} & \text{otherwise} \end{cases}$$
Piecewise((sqrt(3)*atanh(sqrt(3)*sqrt(x)/3)/sqrt(x), (x >= -3)∧(x < 3)), (Sum(3^(-n)*x^n/(1 + 2*n), (n, 0, oo)), True))