Numbers / 18

The Number 18

18 is composite: factorization 2 × 3^2. That gives 18 exactly 6 divisors: 1, 2, 3, 6, 9, 18. 18's proper divisors total 21, 3 more than 18 itself, so 18 is abundant. 18 has a digit sum of 9; for 18, the digital root works out to 9. 18: 2, 3, 6, 9 all divide 18 evenly, out of 2-12. 18 is 10010 in binary and 12 in hex; as a Roman numeral it's XVIII.