There are 4 aces and 16 tens (10/J/Q/K of each suit). So there are (16*4= 64 ways to deal a blackjack with ace as first card and a ten as the second card- Ace/10. There are another 64 ways to deal it with a ten as the first card and the ace as the second card - 10/Ace. That's 128 first/second card combinations that are blackjacks.
There are 52 possibilities for the first card, 51 for the second for 2652 total possible first/second card combinations so the odds of dealing a blackjack are 128/2652, which reduces to 32/663 odds
