b21 := (1,3,5,2)(4,6,9,12)(7,10,14,19)(8,11,16,22)(13,18,25,35)(15,20,28,39)
     (17,23,32,44)(21,29,34,47)(24,33,46,48)(26,36,50,65)(27,37,51,67)(30,41,
     56,72)(31,42,58,60)(38,52,68,74)(40,54,70,82)(43,59,64,62)(45,61,57,73)
     (49,63,76,88)(53,69,81,95)(55,71,84,98)(66,78,91,94)(75,87,102,116)(77,
     89,86,100)(79,92,108,125)(80,93,110,128)(83,96,113,131)(85,99,117,135)
     (90,105,118,136)(97,114,120,134)(101,119,138,143)(103,121,132,141)(104,
     112,106,122)(107,123,115,133)(109,126,130,124)(111,129,137,139)(127,140,
     142,144);