As we mentioned, Blackjack is one of the simplest games on the casino floor side bets add a great deal of complexity to the game, though, inevitably, your odds of winning a side bet are going to be much lower than that of winning a regular hand.
The 21 + 3 blackjack side bet is based on examining the player's two cards and the dealer's up-card. If the three cards form a flush, straight, three-of-a-kind or straight flush, the player wins.