a21 := (1,3,6,10)(2,4,7,12)(5,8,14,21)(9,15,23,32)(11,17,26,36)(13,19,29,41)
     (16,24)(18,27,38,52)(20,22,31,44)(25,34,48,63)(28,39,33,46)(30,42,57,71)
     (35,49,53,37)(40,54,68,82)(43,58,55,69)(45,47,61,75)(50,64,78,88)(51,65,
     77,87)(56,70,76,85)(59,73)(60,74,86,72)(66,79,89,81)(67,80,90,84)(83,91);