C(25,10,2) = 10

Method of Construction: lexicographic greedy covering

Lower Bound: Handbook of Combinatorial Designs section on coverings

  1  2  3  4  5  6  7  8  9 10
  1 11 12 13 14 15 16 17 18 19
  2  3 11 12 20 21 22 23 24 25
  4  5  6  7 13 14 15 20 21 22
  4  5  6  7 16 17 18 23 24 25
  8  9 10 13 14 15 19 23 24 25
  1  8  9 10 16 17 18 20 21 22
  4  5  6  7  8  9 10 11 12 19
  2  3 13 14 15 16 17 18 19 20
  1  2  3  4 19 21 22 23 24 25