b21 := (1,3,6)(2,4,8)(5,9,13)(7,11,16)(10,14,20)(12,17,24)(15,21,18)(19,25,31)
     (22,23,28)(26,32,37)(27,33,39)(29,35,41)(30,34,38)(36,42,47)(40,44,50)
     (43,48,54)(45,51,58)(46,52,60)(49,55,64)(53,61,71)(56,65,76)(57,66,78)
     (59,68,80)(62,72,84)(63,73,86)(67,74,87)(69,81,95)(70,79,92)(75,88,91)
     (77,90,83)(82,96,107)(85,98,109)(89,93,103)(94,104,114)(97,105,115)(99,
     110,120)(100,111,101)(102,112,121)(106,116,123)(108,118,124)(113,122,131)
     (117,125,132)(119,127,134)(126,128,135)(130,133,136);