63

63 = 3² x 7.

63 = 6² + 3³ = 2⁶ – 1.

63 is the smallest number such that the common alphabetical value of its representation in Roman numerals is equal to itself: LXIII -- 12 + 24 + 9 + 9 + 9 = 63.

63 is a Harshad (or Niven) number; that is, it is divisible by the sum of its digits.

63 is the number of partially ordered sets of 5 elements.

63 is 333 in base 4.

M63 is a galaxy, known as the Sunflower Galaxy, in the constellation Canes Venatici.

Source: Number Gossip