lower bound = 37

C(21,4,2) = 37

Method of Construction: induced from projective geometry covering

Lower Bound: Schonheim

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