// atan(4*x) \
|| --------- for And(x >= -1/4, x <= 1/4)|
|| 4*x |
|| |
|| oo |
||____ |
4*x*|<\ ` |
|| \ n 2*n |
|| \ (-16) *x |
|| / ----------- otherwise |
|| / 1 + 2*n |
||/___, |
\\n = 0 /
$$4 x \left(\begin{cases} \frac{\operatorname{atan}{\left(4 x \right)}}{4 x} & \text{for}\: x \geq - \frac{1}{4} \wedge x \leq \frac{1}{4} \\\sum_{n=0}^{\infty} \frac{\left(-16\right)^{n} x^{2 n}}{2 n + 1} & \text{otherwise} \end{cases}\right)$$
4*x*Piecewise((atan(4*x)/(4*x), (x >= -1/4)∧(x <= 1/4)), (Sum((-16)^n*x^(2*n)/(1 + 2*n), (n, 0, oo)), True))