Let A, B ∈ N with A > 1, B > 1 and gcd(A, B) = 1, k ≥ 2 be an integer coprime with AB, and let λ ∈ {1, 2, 4} be such that if λ = 4, then A = 4 and B = 4; and if k is even, then λ = 4. In this paper, we shall describe all solutions of the equationwhere the symbol X| * A means that every prime divisor of X divides A. Then, using this result, we give some more general results on the number of solutions of the equation la x + mb y = λc z , x > 1, y > 1, z > 1. In addition, using Cao's result on Pell equation, we obtain some improvement of Terai's results on the equations a x + 2 = c z , a x + 4 = c z and a x + 2 y = c z .