Numbers / 689

The Number 689

689 is composite: factorization 13 × 53. That gives 689 exactly 4 divisors: 1, 13, 53, 689. 689's proper divisors total just 67, 622 short of 689, the deficient case most of 689's neighbors share too. 689 has a digit sum of 23; for 689, the digital root works out to 5. 689 shares no factor with 2-12; 689's own divisors start beyond that range. 689 is 1010110001 in binary and 2B1 in hex; as a Roman numeral it's DCLXXXIX.