Let R be a perfectoid ring. Hesselholt and Bhatt-Morrow-Scholze have identified the Postnikov filtration on THH(R; Zp): it is concentrated in even degrees, generated by powers of the Bökstedt generator σ, generalizing classical Bökstedt periodicity for R = Fp. We study an equivariant generalization of the Postnikov filtration, the regular slice filtration, on THH(R; Zp). The slice filtration is again concentrated in even degrees, generated by RO(T)-graded classes which can loosely be thought of as the norms of σ. The slices are expressible as RO(T)-graded suspensions of Mackey functors obtained from the Witt Mackey functor. We obtain a sort of filtration by q-factorials. A key ingredient, which may be of independent interest, is a close connection between the Hill-Yarnall characterization of the slice filtration and Anschütz-le Bras' q-deformation of Legendre's formula.