✓ Mathematica : cpu = 0.0376309 (sec), leaf count = 29
DSolve[(1 - a^2)*x*Derivative[1][y][x] + 3*x^2*Derivative[2][y][x] + x^3*Derivative[3][y][x] == 0,y[x],x]
✓ Maple : cpu = 0.012 (sec), leaf count = 18
dsolve(x^3*diff(diff(diff(y(x),x),x),x)+3*x^2*diff(diff(y(x),x),x)+(-a^2+1)*x*diff(y(x),x)=0,y(x))