“…Denote by K q (n, 1, 2) the minimal cardinality of a code C ⊂ Q n with covering radius 1 and minimum distance 2. Well-known results are K q (2, 1, 2) = q and K q (3, 1, 2) = q 2 /2 as well as K 2 (4, 1, 2) = 4, K 2 (5, 1, 2) = 8, K 2 (6, 1, 2) = 12, K 3 (4, 1, 2) = 9, K 4 (4, 1, 2) = 28 and K q (n + 1, 1, 2) ≤ q • K q (n, 1, 2), see [4,3,8,6].…”