Properties6 is an even number, the third triangular number, the third factorial number, and 3 or 4 primorial.
6 is equal to the sum of its unitary proper divisors, that is to say divisors d such that d and n/d are relatively prime. These are called unitary perfect numbers. It is the smallest number with this property.
It is the smallest number N such that all multiples of N are abundant. All perfect or abundant numbers have this property.
In Czech language, 6 is called "půltucet", meaning "half-twelve".
Six is the basis of Robert Munafo's idea of classes. 6 is the boundary between class 0 and class 1 numbers, 106 is the boundary between class 1 and class 2 numbers, 10106 is the boundary between class 2 and class 3 numbers, and so on.
In Greek-based number naming systems, 6 is associated with prefix hexa-, and with prefix sexti- in Latin systems.
6 is the last digit of mega.