Sphere packing

Sphere packing has various applications in error-correcting codes, the channel coding problem, Steiner systems, $t$-designs, and in the theory of finite groups. The most important special case is the sphere packing in $\R^{24}$ via the Leech lattice. Finite and infinite sphere packing in $\R^3$ has applications in classical and modern crystallography.

J.H. Conway, N.J.A. Sloane, "Sphere packing, lattices and groups" , Springer (1988)