\[ y'(x)=x^2 \sqrt {a^2+2 a x+x^2+4 y(x)}-\frac {a}{2}-\frac {x}{2} \] ✓ Mathematica : cpu = 0.258556 (sec), leaf count = 42
\[\left \{\left \{y(x)\to \frac {1}{36} \left (-9 a^2-18 a x-24 c_1 x^3+36 c_1^2+4 x^6-9 x^2\right )\right \}\right \}\]
✓ Maple : cpu = 0.26 (sec), leaf count = 29
\[ \left \{ {\it \_C1}+{\frac {2\,{x}^{3}}{3}}-\sqrt {{x}^{2}+2\,ax+{a}^{2}+4\,y \left ( x \right ) }=0 \right \} \]