“…In recent years, the equation (1.1) has been extensively studied under various assumptions on V and f and there are many interesting results in the literature on the existence and multiplicity of solutions to problem (1.5) has been obtained via variational approaches, we refer the readers to [3,5,7,8,9,11,12,13,17,18,19,20,21,22]. In particular, the existence of infinitely many high or small energy solutions to problem (1.1) was established in [5,7,9,11,12,13,17,19] by the aid of variant fountain theorems (see [24]) or the symmetric mountain pass theorem (see [23]). However, there are few papers concern with the existence of infinitely many (high or small) energy solutions to problem (1.1) in the case where f (x, u) is a combination of sublinear and superlinear terms at infinity with respect to u, see for instance [7,17,20].…”