How many square numbers in a pack of 52 cards?

In a standard pack of 52 playing cards, there are 4 square numbers: 1 (Ace), 4 (4 of any suit), 9 (9 of any suit), and 16 (King of Hearts, as it is sometimes counted as 4, 3, 2, 1). Therefore, there are 4 square numbers in a deck of 52 cards.