Let an denotes the number of outcomes in which no two consecutive head occurs in n tosses clearly a1 = 2 and a2 = 3. Let us consider last outcome is fixed as tail then we cannot have two consecutive heads in first (n – 1) tosses in an−1 ways and if last outcome is head we must have tail at (n – 1)th toss and cannot have two consecutive heads in first (n – 2) tosses in an−2 ways. So,