 Ulam's packing conjecture

Ulam's packing conjecture is a hypothesis in the field of geometry and combinatorial mathematics, particularly concerning the arrangement of spheres in space. Formulated by mathematician Stanislaw Ulam, the conjecture posits that the densest packing of spheres (in three-dimensional space) occurs when the spheres are arranged in a face-centered cubic (FCC) lattice structure or equivalently in a hexagonal close packing (HCP) arrangement.