Izv. Vyssh. Uchebn. Zaved. Mat., 1958 Number 4,Pages 54–59(Mi ivm2948)
Properties of solutions of the differential equation $\dfrac{d^ny}{dx^n}+p(x)\cdot\dfrac{d^{n-1}y}{dx^{n-1}}+q(x)\dfrac{d^{n-2}y}{dx^{n-2}}+f(x)\cdot y=0$ and their derivatives for large values of the argument