a21 := (1,2)(3,4,6,9)(5,7,11,16)(8,12,18,26)(10,14,21,30)(13,19,28,39)(15,22,
     31,44)(17,24,34,36)(20,29,41,55)(23,32,46,61)(25,35,50,60)(27,37,49,64)
     (33,47,63,40)(38,52,66,75)(42,56)(43,57,71,72)(45,59,70,74)(48,54,58,62)
     (51,65,73,69)(53,67,77,68)(76,78);