Numbers / 31

The Number 31

31 is prime: only 1 and 31 divide it evenly; the next prime after 31 is 37. 31's proper divisors total just 1, 30 short of 31, the deficient case most of 31's neighbors share too. 31 has a digit sum of 4; for 31, the digital root works out to 4. 31 shares no factor with 2-12; 31's own divisors start beyond that range. 31 is 11111 in binary and 1F in hex; as a Roman numeral it's XXXI.