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Consider the equation u + u = g(u, p) + µf (t), where p, u are samll parameters, g is an odd smooth nonlinear function of u, f is an even continuous function, either 2π/m-periodic or π/m-odd-harmonic (i.e, f(t + π/m) = -f(t), for every t in R) and m≥ 2 is an integer. Under certain conditions, the small 2π-periodic solutions maintain some symmetry properties of the forcing function f(t), when µ ≠ 0. Some other interesting results describe the changes of the number of such solutions, as p and µ very is a small neighborhood of the origin. It was also proved that a central assumption, which was required in the main results, is generic. The main tool used in this work is the Liapunov-Schmidt Method.