21 ≤ C(21,9,3) ≤ 24

Method of Construction: simple construction: induced on c(22,10,4) covering

Lower Bound: Schonheim

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