The group of symmetries of a regular n‐sided polygon; the notation D2n is often used as the group has order 2n. If r denotes a rotation by 360°/n and s denotes a reflection, then r and s are generators of D2n. The group contains n rotations e,r,r2, …, rn–1 and n reflections s, rs, r2s, …, rn–1s.