Aurifeuillean factorization
In number theory, an aurifeuillean factorization, named after Léon-François-Antoine Aurifeuille, is factorization of certain integer values of the cyclotomic polynomials. Because cyclotomic polynomials are irreducible polynomials over the integers, such a factorization cannot come from an algebraic factorization of the polynomial.
Source: Wikipedia — Aurifeuillean factorization (CC BY-SA 4.0)