252 = 2 x 2 x 3 x 3 x 7.
252 is the smallest number that is the product of two distinct numbers that are reverse of each other: 252 = 12 x 21.
252 = 28 - 4.
252 is the third value of Ramanujan's tau function (A000594).
252 is a hexagonal pyramidal number.
If you flip a coin 10 times in a row, there are exactly 252 ways in which it can turn out that you get exactly five heads and five tails.
Source: Number Gossip