Swinnerton-Dyer polynomial
In algebra, the Swinnerton-Dyer polynomials are a family of polynomials, introduced by Peter Swinnerton-Dyer, that serve as examples where polynomial factorization algorithms have worst-case runtime. They have the property of being reducible modulo every prime, while being irreducible over the rational numbers.
Source: Wikipedia — Swinnerton-Dyer polynomial (CC BY-SA 4.0)