16 ≤ C(21,10,3) ≤ 18

Method of Construction: simple construction: induced on c(22,11,4) covering

Lower Bound: Horsley-Singh, Theorem 6, s=1

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