b21 := (1,2,3)(5,6,7)(8,10,11)(9,12,13)(14,18,19)(15,20,21)(16,22,23)(17,24,25)
     (26,30,31)(27,32,33)(28,34,35)(29,36,37)(38,44,45)(41,46,47)(42,48,49)
     (43,50,51)(52,53,54);