Source: /cirosantilli/dihedral-group

= Dihedral group
{title2=$D_n$}
{wiki}

Our notation: $D_n$, called "dihedral group of degree n", means the dihedral group of the <regular polygon> with $n$ sides, and therefore has order $2n$ (all rotations + flips), called the "dihedral group of <order (algebra)> 2n".