What card game does Raymond master in "Rain Man"?

Raymond can keep a running tally of every single card like a human calculator, which makes him the perfect companion at the blackjack table. The brothers hit up Caesars Palace and Raymond's photographic memory transforms what should be a game of chance into a math equation he can solve in real time. Charlie teaches him the basics of when to hit and when to stay, but Raymond's brain does all the heavy lifting by tracking which cards are still in the deck. The scheme works until the casino figures out what's happening and "politely" suggests they take their winnings and get lost. Dustin Hoffman got so caught up in the role that he kept sneaking off to play actual blackjack between takes. Too bad he couldn't bring his character's skills with him.