20 = 22 x 5.
20 is the smallest number that cannot be prefixed or followed by one digit to form a prime.
20 has a representation as a sum of two squares: 20 = 42 + 22.
20 is 22 in base 9.
An icosahedron is a polyhedron with 20 triangular faces. The prefix icos comes from the Greek word for “twenty.”
