EN
We investigate the exponent of convergence of the zero-sequence of solutions of the differential equation
$f^{(k)} + a_{k-1}(z)f^{(k-1)} + ⋯ + a₁(z)f' +D(z)f=0$, (1)
where $D(z) = Q₁(z)e^{P₁(z)} + Q₂(z)e^{P₂(z)} + Q₃(z)e^{P₃(z)}$, P₁(z),P₂(z),P₃(z) are polynomials of degree n ≥ 1, Q₁(z),Q₂(z),Q₃(z),$a_j(z)$ (j=1,..., k-1) are entire functions of order less than n, and k ≥ 2.