Numbers / 685

The Number 685

685 is composite: factorization 5 × 137. That gives 685 exactly 4 divisors: 1, 5, 137, 685. 685's proper divisors total just 143, 542 short of 685, the deficient case most of 685's neighbors share too. 685 has a digit sum of 19; for 685, the digital root works out to 1. 685: 5 all divide 685 evenly, out of 2-12. 685 is 1010101101 in binary and 2AD in hex; as a Roman numeral it's DCLXXXV.