DSolve[(1 - 4*a^2*nu^2 + 4*a^2*x^(2*a))*Derivative[1][y][x] + 3*x*Derivative[2][y][x] + x^2*Derivative[3][y][x] == 4*a^3*x^(-1 + 2*a)*y[x],y[x],x]