Numbers / 409

The Number 409

409 is prime: only 1 and 409 divide it evenly; the next prime after 409 is 419. 409's proper divisors total just 1, 408 short of 409, the deficient case most of 409's neighbors share too. 409 has a digit sum of 13; for 409, the digital root works out to 4. 409 shares no factor with 2-12; 409's own divisors start beyond that range. 409 is 110011001 in binary and 199 in hex; as a Roman numeral it's CDIX.