If there is a common factor f, the double rotation can be written as 1 ⁄ f [2 pf,2,2 qf ] (with gcd (p, q)=1), generators {0123,0132}, order 2 pqf. For example, p = q =1, f =2, 1 ⁄ 2 [4,2,4 ] is order 4. And 1 ⁄ f [2 pf,2,2 qf ], generator {0123}, is order pqf. For example, 1 ⁄ 2 [4,2,4 ] is order 2, a central inversion.