C(21,12,2) = 5

Method of Construction: lex covering

Lower Bound: Bounds for fixed number of blocks

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