Numbers / 647

The Number 647

647 is prime: only 1 and 647 divide it evenly; the next prime after 647 is 653. 647's proper divisors total just 1, 646 short of 647, the deficient case most of 647's neighbors share too. 647 has a digit sum of 17; for 647, the digital root works out to 8. 647 shares no factor with 2-12; 647's own divisors start beyond that range. 647 is 1010000111 in binary and 287 in hex; as a Roman numeral it's DCXLVII.