27 ≤ C(21,11,4) ≤ 31

Method of Construction: induced from affine geometry covering

Lower Bound: Schonheim

  2  5  6  7  8  9 11 13 14 18 21
  1  2  4  5 10 11 12 14 17 18 20
  1  2  3  7  9 10 13 14 17 18 19
  3  4  6  9 11 14 16 17 18 20 21
  3  4  5  8 11 12 13 15 16 19 21
  1  8  9 10 11 12 14 15 17 19 21
  2  3  8  9 10 11 12 13 16 18 20
  1  2  6  8 14 15 16 17 18 20 21
  1  4  5  6  8  9 10 14 16 19 20
  1  2  3  4  7 10 11 15 16 19 21
  2  3  4  5  6  9 10 13 15 18 21
  5  6  7 10 12 13 14 16 18 19 21
  1  3  5  7  9 11 15 16 18 19 20
  3  5  6  8  9 12 14 15 16 17 18
  1  2  5  9 12 13 16 17 19 20 21
  2  4  6  7  9 12 13 14 15 16 20
  4  7  8 10 11 13 14 15 18 19 20
  1  2  4  6  8  9 11 13 15 17 19
  4  5  6  7  9 10 11 12 15 17 20
  2  3  4  8 10 12 14 17 19 20 21
  4  7  8  9 10 12 15 16 17 20 21
  1  3  4  6  7  8  9 12 18 19 21
  2  4  5  7  8  9 16 17 18 19 21
  2  3  5  6 10 11 14 15 16 17 19
  2  6  7 11 12 15 17 18 19 20 21
  1  5  6  8 10 11 13 17 18 20 21
  1  3  4  6  8 12 13 15 16 19 20
  1  4  6 10 11 12 13 15 16 17 18
  1  2  3  5  6  7  8 10 12 15 20
  1  3  4  5  7 13 14 15 17 20 21
  1  3  6  7  8 11 12 13 14 16 17