b21 := (1,3,6,10)(2,4,7,12)(5,8,14,21)(9,15,23,34)(11,17,26,38)(13,19,29,43)
     (16,24,25,36)(18,27,40,56)(20,30,45,62)(22,32,48,67)(28,41,57,61)(31,46,
     64,82)(33,49,69,88)(35,51)(37,53,74,94)(39,54,76,96)(42,58,59,79)(44,60)
     (47,65,84,103)(50,70,90,73)(52,72,93,115)(55,77,98,118)(66,85,105,125)
     (68,87,108,130)(71,91,113,112)(75,78,99,120)(81,101,122,138)(83,102,123,
     140)(86,106,127,144)(89,110,131,92)(95,111,132,147)(97,117,134,104)(100,
     114)(107,128,145,158)(116,133,119,135)(121,136,150,161)(124,141,154,164)
     (126,143,157,153)(129,137)(139,151,162,156)(142,155,166,171)(146,159,167,
     169)(148,152,163,168)(149,160)(165,170,172,175)(173,176);