// -n2 |n2| \
|| ---------- for ---- < 1|
|| / n2\ 3 |
|| 3*|1 + --| |
|| \ 3 / |
|| |
n2*|< oo |
|| ___ |
|| \ ` |
|| \ n -n n |
|| / (-1) *3 *n2 otherwise |
|| /__, |
\\n = 1 /
---------------------------------------
3
$$\frac{n_{2} \left(\begin{cases} - \frac{n_{2}}{3 \left(\frac{n_{2}}{3} + 1\right)} & \text{for}\: \frac{\left|{n_{2}}\right|}{3} < 1 \\\sum_{n=1}^{\infty} \left(-1\right)^{n} 3^{- n} n_{2}^{n} & \text{otherwise} \end{cases}\right)}{3}$$
n2*Piecewise((-n2/(3*(1 + n2/3)), |n2|/3 < 1), (Sum((-1)^n*3^(-n)*n2^n, (n, 1, oo)), True))/3