12 = 22 x 3.
12 is the sum of the first three even integers and the sum of thee consecutive odd integers: 12 = 2 + 4 + 6 = 3 + 4 + 5.
A regular dodecahedron has a regular pentagon on each of its 12 faces.
12 has a unique representation as a sum of three squares: 12 = 22 + 22 + 22.
12 is the number of integer partitions of 11 into distinct parts.
12 is 22 in base 5.
There are 12 ways to arrange eight queens on a chessboard so that no queen can capture any other queen (not counting rotations and reflections as being different). Can you find one of these chessboard arrangements?
12 is a dozen. There are 12 months in a year and 12 inches in a foot; 12 o'clock is midday or midnight. There are 12 signs of the Zodiac, 12 apostles, and typically 12 people in a jury.
Source: Phillips, R. 1994. Numbers: Facts, Figures and Fiction. Cambridge University Press.