/ / / x\\
| | 18*log|1 - -||
| | 2 \ 3/|
|x*|- -------- + -------------|
| | 2 2 |
| | x x x |
| | - - + -- |
| \ 3 9 / |x|
|------------------------------ for --- < 1
| 6 3
<
| oo
| ____
| \ `
| \ -n n
| \ n*3 *x
| / -------- otherwise
| / 1 + n
| /___,
| n = 0
\
$$\begin{cases} \frac{x \left(- \frac{2}{\frac{x^{2}}{9} - \frac{x}{3}} + \frac{18 \log{\left(1 - \frac{x}{3} \right)}}{x^{2}}\right)}{6} & \text{for}\: \frac{\left|{x}\right|}{3} < 1 \\\sum_{n=0}^{\infty} \frac{3^{- n} n x^{n}}{n + 1} & \text{otherwise} \end{cases}$$
Piecewise((x*(-2/(-x/3 + x^2/9) + 18*log(1 - x/3)/x^2)/6, |x|/3 < 1), (Sum(n*3^(-n)*x^n/(1 + n), (n, 0, oo)), True))