Six is the smallest perfect number as it is equal to the sum of its proper divisors (1 , 2 and 3).

Six is the only number that is both the sum and the product of three consecutive positive numbers.

Also:

• A hexagon has 6 sides
• A tetrahedron has 6 edges
• An octahedron and a tetrahemihexahedron have 6 vertices
• A truncated cube, a small cubicuboctahedron, a cubitruncated cuboctahedron, and small rhombihexahedron have 6 octagons
• A cube, a truncated octahedron, a cuboctahedron, a snub cube, a small cubicuboctahedron, a great cubicuboctahedron, and a cubohemioctahedron have 6 squares
• A great cubicuboctahedron, a cubitruncated cuboctahedron, a quasitruncated hexahedron, a quasitruncated cuboctahedron, and a great rhombihexahedron have 6 octagrams
• A small icosahemidodecahedron and a small dodecahemidodecahedron have 6 decagons
• A great icosahemidodecahedron and a great dodecahemidodecahedron have 6 decagrams
• 6 is the factorial of 3 ($3! = 6$)
• 6 is a triangular number
• 6 is a hexagonal number
• 6 is an octahedral number
• 6 is a palindromic number
• 6 is a pronic number.