lower bound = 21

C(21,5,2) = 21

Method of Construction: cyclic covering found by search program

Lower Bound: Schonheim

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