You would need to roll a regular die at least 7 times to be sure that at least one number will be repeated. This is because there are 6 possible outcomes when rolling a die (numbers 1 through 6), and the pigeonhole principle states that if you have n items to place in m containers, and n > m, then at least one container must contain more than one item. In this case, rolling a die 6 times would cover all possible outcomes without a repeat, so rolling it one more time would guarantee a repeated number.
