where the nonlinearity
g has a repulsive singularity at the origin. In previous papers dealing with this kind
of problem it is usually assumed a nonintegrability condition on
g near the origin. We provide a weaker condition that substitutes the nonintegrability
of g. If
f≡0 the existence
of subharmonic solutions is proved utilizing a variational method and when
f≠0 we prove the existence
of a periodic solution using topological
degree theory.