Cards are drawn from a standard 52-card deck. After each card is drawn, it is put back in the deck and the cards are reshuffled so that each card drawn is independent of all others.
Let be the random variable that represents the number of cards that are drawn before the second appearance of an ace.
For example, if the sequence of cards drawn was {2, 5, K, 7, A, 5, 3, J, A, ...}, hen would take on a value of 8.
Find the probability mass function of . That is, find 