A clinic appointment system forms a 3-digit tag p_1 p_2 p_3 using digits 1, 2, 3, 4, 5, 6, 7 (4 odd digits and 3 even digits). Tags must have odd digits in odd positions (p_1 and p_3), and adjacent digits must differ (p_2 ≠ p_1 and p_3 ≠ p_2).