21 ≤ C(28,7,2) ≤ 22
Method of Construction: simple construction: induced on c(29,8,3) covering
Lower Bound: Horsley, Theorem 1, r=5, d=3
1 2 4 14 16 21 26
3 13 15 20 21 22 25
1 2 11 13 18 19 28
10 12 17 18 21 27 28
9 11 16 17 20 26 27
8 10 15 16 19 25 26
7 9 14 15 18 25 28
6 8 13 14 17 24 27
5 7 12 13 16 23 26
4 6 11 12 15 24 25
3 5 10 11 14 22 23
3 12 14 18 19 20 28
3 4 9 10 13 16 26
3 6 7 8 11 21 24
1 2 3 8 9 12 22
1 2 6 7 10 20 24
5 6 9 19 21 23 24
4 5 8 18 20 23 28
3 4 7 17 19 22 27
6 16 18 22 24 26 28
2 5 15 17 23 25 27
1 5 15 17 23 25 27