Numbers / 641

The Number 641

641 is prime: only 1 and 641 divide it evenly; the next prime after 641 is 643. 641's proper divisors total just 1, 640 short of 641, the deficient case most of 641's neighbors share too. 641 has a digit sum of 11; for 641, the digital root works out to 2. 641 shares no factor with 2-12; 641's own divisors start beyond that range. 641 is 1010000001 in binary and 281 in hex; as a Roman numeral it's DCXLI.