When the number is 1, 2, 3, ..., n, the lottery will not be put back. If 1 is the winning number, the lottery will be held at the k th time (1≤k≤n).

From the n prize volumes of 1, 2, 3, ..., n, all the methods for extracting k prize volumes of 1≤k≤n are as follows:

(n- 1)(n-2)(n-3)..(n-k+ 1)

From the probability formula of classical probability

P=(n？ 1)(n？ 2)(n？ 3)..(n？ k+ 1)n(n？ 1)(n？ 2)(n？ 3)..(n？ k+ 1)= 1n。

So the answer is1n.