Almost periodic sequence

Summary

An almost periodic sequence is a bounded sequence that comes back arbitrarily close to itself after shifts that occur regularly. It need not repeat exactly. It is the discrete version, in the sense of Harald Bohr, of an almost periodic function. Every periodic sequence is almost periodic, and so is every sum of finitely many sequences $e^{i \lambda n}$. Almost periodic sequences arise as solutions of difference equations with almost periodic coefficients or forcing.