Six (6) is a positive integer one more than 5 and one less than 7.
6 is the second composite number and the first to not be a power. Its factorization is 2*3. The next composite number is 8 and the previous is 4. It is the second semiprime number, between 4 and 9.
6 is the third triangular number (between 3 and 10).
6 is the third factorial number, between 2 and 24. It is also the second primorial number (between 2 and 30). It is the only number after 2 to be both a factorial and primorial.
6 is the first perfect number, because 1+2+3 = 6. The next perfect number is 28.
6 is the fourth highly composite number, the first with 4 factors. The next is 12 and the previous is 4.