/ / 4*x / x\\
| | -2 + --- 18*log|1 - -||
| | 3 \ 3/|
|x*|--------------- - -------------|
| | 2 3 2 |
| | 2*x x x x |
| |- ---- + - + -- |
| \ 9 3 27 / |x|
|----------------------------------- for --- < 1
| 6 3
<
| oo
| ____
| \ `
| \ -n 2 n
| \ 3 *n *x
| / --------- otherwise
| / 1 + n
| /___,
| n = 1
\
$$\begin{cases} \frac{x \left(\frac{\frac{4 x}{3} - 2}{\frac{x^{3}}{27} - \frac{2 x^{2}}{9} + \frac{x}{3}} - \frac{18 \log{\left(1 - \frac{x}{3} \right)}}{x^{2}}\right)}{6} & \text{for}\: \frac{\left|{x}\right|}{3} < 1 \\\sum_{n=1}^{\infty} \frac{3^{- n} n^{2} x^{n}}{n + 1} & \text{otherwise} \end{cases}$$
Piecewise((x*((-2 + 4*x/3)/(-2*x^2/9 + x/3 + x^3/27) - 18*log(1 - x/3)/x^2)/6, |x|/3 < 1), (Sum(3^(-n)*n^2*x^n/(1 + n), (n, 1, oo)), True))