Numbers / 691

The Number 691

691 is prime: only 1 and 691 divide it evenly; the next prime after 691 is 701. 691's proper divisors total just 1, 690 short of 691, the deficient case most of 691's neighbors share too. 691 has a digit sum of 16; for 691, the digital root works out to 7. 691 shares no factor with 2-12; 691's own divisors start beyond that range. 691 is 1010110011 in binary and 2B3 in hex; as a Roman numeral it's DCXCI.