Although set in the then-present day, i.e. 2007/8, the film is based on teams active between 1979 and 1994. And at one point, more than 80 players were on the original MIT team.
According to Kevin Spacey, as part of their research for the film, they took some of the real players who were on the original team to Vegas. Although they weren't allowed to play, every time they wanted Spacey to up his bet, they would push up against his chair. He said, "I would win every time!"
The main characters upon which the film 21 is based were Asian. Controversially, mostly Caucasian actors were cast. Jim Sturgess required a dialect coach to speak with an American accent.
Boston University students were used as extras in many of the classroom scenes.
The problem that professor Rosa explains in class with the three doors is known as the Monty Hall problem, named after the host of the game show Let's Make a Deal (1963) who would provide candidates with the same set of options. It is an example of a veridical paradox, where the best course of action is usually not taken because it feels intuitively wrong. As Ben correctly points out (and something ultimately proven in simulations), switching to the other door indeed gives a 2/3 change of success, versus 1/3 for staying with the original choice.
Jeff Ma: The real-life inspiration behind the character Ben Campbell as a Planet Hollywood blackjack dealer, referred to by Ben Campbell as 'my brother from another mother'.
Gustaf Skarsgård: Long-haired man working for Cole Williams. He can be seen chasing Ben in the final run out of the casino.
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