The third derivative
[src]
/ 2 2 \
6 | 2 28 72*x*atan(3*x) 36*x *atan (3*x)|
54*atan (3*x)*|- atan (3*x) + -------- - -------------- + ----------------|
| 2 2 2 |
\ 1 + 9*x 1 + 9*x 1 + 9*x /
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2
/ 2\
\1 + 9*x /
$$\frac{54 \left(\frac{36 x^{2} \operatorname{atan}^{2}{\left(3 x \right)}}{9 x^{2} + 1} - \frac{72 x \operatorname{atan}{\left(3 x \right)}}{9 x^{2} + 1} - \operatorname{atan}^{2}{\left(3 x \right)} + \frac{28}{9 x^{2} + 1}\right) \operatorname{atan}^{6}{\left(3 x \right)}}{\left(9 x^{2} + 1\right)^{2}}$$