lower bound = 21

21 ≤ CC(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