C(21,8,2) = 11

Method of Construction: lex covering

Lower Bound: Handbook of Combinatorial Designs section on coverings

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