b21 := (1,3)(2,4,7,11)(5,8,13,18)(6,9,15,21)(10,14,19,26)(12,17,23,30)(16,22,
     29,38)(20,27,35,45)(24,31,40,50)(25,32)(28,36,46,59)(33,42,53,69)(34,43,
     55,68)(37,47,61,77)(39,49,54,70)(41,51,66,84)(44,56,72,89)(48,62,79,97)
     (52,67,86,105)(57,73,60,76)(58,74,91,112)(63,80)(64,81,99,121)(65,82,101,
     124)(71,88,108,133)(75,92,114,137)(78,95,117,141)(83,102,125,148)(85,104,
     128,152)(87,106,130,155)(90,110,116,139)(93,103,126,150)(94,115,132,111)
     (96,118,138,165)(98,119)(100,122,144,156)(107,131,157,185)(109,134,160,
     187)(113,136,163,192)(120,140,167,196)(123,145,172,201)(127,151,178,209)
     (129,153,181,211)(135,161,189,219)(142,169,197,225)(143,170,199,222)(146,
     173,203,159)(147,174)(149,175,206,230)(154,182)(162,190)(164,193,223,240)
     (166,195)(168,180,210,232)(171,179)(176,207,231,194)(177,204,216,238)
     (183,212,235,246)(184,213)(186,215,237,214)(188,217,205,229)(191,221,239,
     224)(198,226)(200,227,242,249)(202,228,243,248)(208,218)(233,234,244,241)
     (236,247,245,250);