\[ y'(x)=\frac {x \left (a^3 x^{12}+24 a^2 x^8 y(x)-32 a^2 x^6+192 a x^4 y(x)^2-256 a x^2 y(x)-256 a x^2+512 y(x)^3\right )}{64 a x^4+512 y(x)+512} \] ✓ Mathematica : cpu = 0.0279842 (sec), leaf count = 63
\[\left \{\left \{y(x)\to \frac {512}{\sqrt {c_1-262144 x^2}-512}-\frac {a x^4}{8}\right \},\left \{y(x)\to -\frac {a x^4}{8}-\frac {512}{\sqrt {c_1-262144 x^2}+512}\right \}\right \}\]
✓ Maple : cpu = 0.068 (sec), leaf count = 79
\[ \left \{ y \left ( x \right ) ={1 \left ( -8+ \left ( -\sqrt {-{x}^{2}+{\it \_C1}}-1 \right ) a{x}^{4} \right ) \left ( 8+8\,\sqrt {-{x}^{2}+{\it \_C1}} \right ) ^{-1}},y \left ( x \right ) ={1 \left ( 8+ \left ( -\sqrt {-{x}^{2}+{\it \_C1}}+1 \right ) a{x}^{4} \right ) \left ( -8+8\,\sqrt {-{x}^{2}+{\it \_C1}} \right ) ^{-1}} \right \} \]