Dihedral group

In mathematics, a dihedral group is the group of symmetries of a regular polygon, which includes rotations and reflections. Dihedral groups are among the simplest examples of finite groups, and they play an important role in group theory, geometry, and chemistry.

Algebraic structure → Group theory
Group theory
Basic notions
  • Subgroup
  • Normal subgroup
Group homomorphisms
Finite groups
  • Schur multiplier
Classification of finite simple groups
Modular groups
  • PSL(2, )
  • SL(2, )
Topological and Lie groups
  • Special linear SL(n)
  • Orthogonal O(n)
  • Special orthogonal SO(n)
  • Unitary U(n)
  • Special unitary SU(n)
  • Symplectic Sp(n)
Infinite dimensional Lie group
  • O(∞)
  • SU(∞)
  • Sp(∞)
Algebraic groups
  • Linear algebraic group
  • Reductive group

The notation for the dihedral group differs in geometry and abstract algebra. In geometry, Dn or Dihn refers to the symmetries of the n-gon, a group of order 2n. In abstract algebra, D2n refers to this same dihedral group. This article uses the geometric convention, Dn.

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