b21 := (1,2,3)(5,6,7)(8,10,11)(9,12,13)(14,17,18)(15,19,20)(16,21,22)(23,28,26)
     (24,29,30)(25,31,32)(27,33,34)(36,42,43)(38,44,45)(39,46,47)(40,48,49)
     (41,50,51)(52,55,54)(53,56,57);