b21 := (1,2,3)(4,6,7)(8,10,11)(9,12,13)(14,17,18)(15,19,20)(16,21,22)(23,28,29)
     (24,30,27)(25,31,32)(26,33,34)(35,42,43)(36,44,45)(38,46,47)(39,48,49)
     (41,50,51)(52,55,54)(53,56,57);