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