15 ≤ C(20,12,4) ≤ 20

Method of Construction: cyclic covering found by search program

Lower Bound: Schonheim

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