X ( 2 , 7 , 3 , 8 ) X ( 4 , 16 , 5 , 15 ) X ( 6 , 18 , 1 , 17 ) X ( 8 , 1 , 9 , 2 ) X ( 10 , 20 , 11 , 19 ) X ( 12 , 14 , 7 , 13 ) X ( 14 , 4 , 15 , 3 ) X ( 16 , 6 , 17 , 5 ) X ( 18 , 10 , 19 , 9 ) X ( 20 , 12 , 13 , 11 ) {\displaystyle X(2,7,3,8)X(4,16,5,15)X(6,18,1,17)X(8,1,9,2)X(10,20,11,19)X(12,14,7,13)X(14,4,15,3)X(16,6,17,5)X(18,10,19,9)X(20,12,13,11)}