Zeros of solutions of certain second order linear differential equation

In this paper, we investigate the exponent of convergence of the zero-sequence of solutions of the differential equationequation(1.3)f″+(Q1eP1(z)+Q2eP2(z)+Q3eP3(z))f=0,f″+(Q1eP1(z)+Q2eP2(z)+Q3eP3(z))f=0, where P1(z)P1(z), P2(z)P2(z), P3(z)P3(z) are polynomials of degree n⩾1n⩾1, Q1Q1, Q2Q2, Q3Q3 are entire functions of order less than n.