lower bound = 13

C(13,4,2) = 13

Method of Construction: cyclic covering found by a search program

Lower Bound: Schonheim

  2  3  5 11
  3  4  6 12
  4  5  7 13
  1  5  6  8
  2  6  7  9
  3  7  8 10
  4  8  9 11
  5  9 10 12
  6 10 11 13
  1  7 11 12
  2  8 12 13
  1  3  9 13
  1  2  4 10