Numbers / 19

The Number 19

19 is prime: only 1 and 19 divide it evenly; the next prime after 19 is 23. 19's proper divisors total just 1, 18 short of 19, the deficient case most of 19's neighbors share too. 19 has a digit sum of 10; for 19, the digital root works out to 1. 19 shares no factor with 2-12; 19's own divisors start beyond that range. 19 is 10011 in binary and 13 in hex; as a Roman numeral it's XIX.