Values of coefficients of cyclotomic polynomials

Let a(k,n)a(k,n) be the kk-th coefficient of the nn-th cyclotomic polynomials. In 1987, J. Suzuki proved that {a(k,n)|n,k∈N}=Z. In this paper, we improve this result and prove that for any prime pp and any integer l≥1l≥1, we have {a(k,pln)∣n,k∈N}=Z.{a(k,pln)∣n,k∈N}=Z.