Numbers / 721

The Number 721

721 is composite: factorization 7 × 103. That gives 721 exactly 4 divisors: 1, 7, 103, 721. 721's proper divisors total just 111, 610 short of 721, the deficient case most of 721's neighbors share too. 721 has a digit sum of 10; for 721, the digital root works out to 1. 721: 7 all divide 721 evenly, out of 2-12. 721 is 1011010001 in binary and 2D1 in hex; as a Roman numeral it's DCCXXI.