M = {17, 18, 19, 20, 21, 22}
We have shown {M ∈ N | 16 < M < 23}. In common English usage, "between 16 and 23" would usually be interpreted as 16 ≤ M ≤ 23. Without additional information, the word "between" makes the problem statement ambiguous. The answer might be M = {16, 17, 18, 19, 20, 21, 22, 23}, depending on the interpretation used by your text and/or instructor.
We have shown {M ∈ N | 16 < M < 23}. In common English usage, "between 16 and 23" would usually be interpreted as 16 ≤ M ≤ 23. Without additional information, the word "between" makes the problem statement ambiguous. The answer might be M = {16, 17, 18, 19, 20, 21, 22, 23}, depending on the interpretation used by your text and/or instructor.