Numbers / 221

The Number 221

221 is composite: factorization 13 × 17. That gives 221 exactly 4 divisors: 1, 13, 17, 221. 221's proper divisors total just 31, 190 short of 221, the deficient case most of 221's neighbors share too. 221 has a digit sum of 5; for 221, the digital root works out to 5. 221 shares no factor with 2-12; 221's own divisors start beyond that range. 221 is 11011101 in binary and DD in hex; as a Roman numeral it's CCXXI.