X ( 2 , 17 , 3 , 18 ) X ( 4 , 14 , 5 , 13 ) X ( 6 , 9 , 7 , 10 ) X ( 8 , 16 , 1 , 15 ) X ( 10 , 1 , 11 , 2 ) X ( 12 , 4 , 13 , 3 ) X ( 14 , 8 , 15 , 7 ) X ( 16 , 12 , 17 , 11 ) X ( 18 , 5 , 9 , 6 ) {\displaystyle X(2,17,3,18)X(4,14,5,13)X(6,9,7,10)X(8,16,1,15)X(10,1,11,2)X(12,4,13,3)X(14,8,15,7)X(16,12,17,11)X(18,5,9,6)}
