30

30 = 2 x 3 x 5.

30 is the smallest number with three distinct prime divisors.

30 has a unique representation as a sum of three squares: 30 = 1² + 2² + 5².

30 is a pyramidal number (the sum of all squares of integers from 1 to 4): 30 = 1² + 2² + 3² + 4².

30 is 33 in base 9.

A dodecahedron is a Platonic solid with 30 edges.


Source: Number Gossip