C(20,13,3) = 8

Method of Construction: dynamic programming covering

Lower Bound: Handbook of Combinatorial Designs section on coverings

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