Is 21 the same as Blackjack?

Yes, 21 and Blackjack are different names for the same game with the rules and payouts being the same. Also, a game event where you make a hand of 21 is called ‘blackjack’ and results in a 6:5 or 3:2 payout, depending on the game version. It's not hard to guess that the 3:2 payout version is more lucrative.