n20
1,2,3,4,5,6;
0,5,6,7,8,9;
0,3,5,10,11,12;
0,2,6,10,13,14;
0,7,11,13,15,16;
0,1,2,8,12,15;
0,1,3,9,14,16;
1,4,8,9,17,18;
1,5,7,12,16,17;
1,6,7,14,15,18;
2,3,11,14,15,19;
2,4,10,12,17,19;
2,5,8,11,13,17;
3,4,12,15,16,18;
3,6,9,10,18,19;
4,5,9,10,13,16;
4,6,8,13,15,19;
7,8,11,12,18,19;
7,9,13,14,17,19;
10,11,14,16,17,18.