PermutationGroup<21|
\[2,1,3,6,7,4,5,12,14,15,17,8,19,9,10,16,11,18,13,20,21
],
\[1,3,5,2,4,8,10,13,6,16,7,18,9,20,14,11,19,12,17,21,15
]
/*order=20160=2^6*3^2*5*7*/>
