Numbers / 821

The Number 821

821 is prime: only 1 and 821 divide it evenly; the next prime after 821 is 823. 821's proper divisors total just 1, 820 short of 821, the deficient case most of 821's neighbors share too. 821 has a digit sum of 11; for 821, the digital root works out to 2. 821 shares no factor with 2-12; 821's own divisors start beyond that range. 821 is 1100110101 in binary and 335 in hex; as a Roman numeral it's DCCCXXI.