EN
Let G be a locally compact second countable Abelian group. Given a measure preserving action T of G on a standard probability space (X,μ), let ℳ (T) denote the set of essential values of the spectral multiplicity function of the Koopman representation $U_{T}$ of G defined in L²(X,μ) ⊖ ℂ by $U_{T}(g)f:= f ∘ T_{-g}$. If G is either a discrete countable Abelian group or ℝⁿ, n ≥ 1, it is shown that the sets of the form {p,q,pq}, {p,q,r,pq,pr,qr,pqr} etc. or any multiplicative (and additive) subsemigroup of ℕ are realizable as ℳ (T) for a weakly mixing G-action T.