Numbers / 401

The Number 401

401 is prime: only 1 and 401 divide it evenly; the next prime after 401 is 409. 401's proper divisors total just 1, 400 short of 401, the deficient case most of 401's neighbors share too. 401 has a digit sum of 5; for 401, the digital root works out to 5. 401 shares no factor with 2-12; 401's own divisors start beyond that range. 401 is 110010001 in binary and 191 in hex; as a Roman numeral it's CDI.