// /15 2 \ \
|| |-- - 5*x / 2\ | |
|| 4 |2 \-15 + 15*x /*atanh(x)| |
||x *|--------- + ----------------------| |
|| | 4 5 | |
|| \ x 2*x / | 2| |
||--------------------------------------- for |x | <= 1|
|| 15 |
|| |
x*|< oo |
|| ____ |
|| \ ` |
|| \ 2*n |
|| \ x |
|| ) --------- otherwise |
|| / 2 |
|| / -1 + 4*n |
|| /___, |
\\ n = 2 /
$$x \left(\begin{cases} \frac{x^{4} \left(\frac{\frac{15}{2} - 5 x^{2}}{x^{4}} + \frac{\left(15 x^{2} - 15\right) \operatorname{atanh}{\left(x \right)}}{2 x^{5}}\right)}{15} & \text{for}\: \left|{x^{2}}\right| \leq 1 \\\sum_{n=2}^{\infty} \frac{x^{2 n}}{4 n^{2} - 1} & \text{otherwise} \end{cases}\right)$$
x*Piecewise((x^4*((15/2 - 5*x^2)/x^4 + (-15 + 15*x^2)*atanh(x)/(2*x^5))/15, |x^2| <= 1), (Sum(x^(2*n)/(-1 + 4*n^2), (n, 2, oo)), True))