b21 := (1,2,5,3)(4,7,12,8)(6,10)(9,14,19,15)(13,18)(16,21,26,20)(17,22,28,23)
     (24,30,39,31)(25,32,29,33)(27,35,41,36)(34,42,45,43)(37,44)(38,40,48,46)
     (47,49);