lower bound = 20

20 ≤ CC(12,7,4) ≤ 24

Method of Construction: nurmela and ostergard simulated annealing cover

Lower Bound: Theorem 2.1 of Mills and Mullin; r=2

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