On the period of sums of discrete periodic signals

Unlike the continuous case, given two discrete periodic signals, their sum is always periodic. We give a characterization for the period of the sum; as shown, the least common multiple of the periods of the signals being added is not necessarily the period of the sum. Number theoretical proofs are given for the sake of rigor; examples and an interpretation in the Fourier frequency domain are given for the sake of intuition and applications.