The special form of Riccati equation 
$$
\frac{\mathrm{d} y}{\mathrm{d} x} =ax^{m}+by^{2}
$$ has been proved that it is solvable if and only if $m=0$, $m=-2$, $m=4k/(2k\pm 1)$.<br>
The sufficiency is obviously. But how to prove its necessity?