This question is making me lose my mind. The probability of n number of events occurring is modeled by the random variable P(N = n) = 1/((n + 1)(n+2)

And I need to find the probability of at least one happening given that not more than 4 have occurred.

The way I did it is just by calculating P(1 <= n <= 4) = 1/3, but this isn't the correct answer. What did I do wrong?