We study the problem of existence and multiplicity of subharmonic solutions for a second order nonlinear ODE in presence of lower and upper solutions. We show how such additional information can be used to obtain more precise multiplicity results. Applications are given to pendulum type equations and to Ambrosetti-Prodi results for parameter dependent equations.

%B Discrete & Continuous Dynamical Systems - A %V 33 %P 89 %G eng %U http://aimsciences.org//article/id/3638a93e-4f3e-4146-a927-3e8a64e6863f %R 10.3934/dcds.2013.33.89