Numbers / 51

The Number 51

51 is composite: factorization 3 × 17. That gives 51 exactly 4 divisors: 1, 3, 17, 51. 51's proper divisors total just 21, 30 short of 51, the deficient case most of 51's neighbors share too. 51 has a digit sum of 6; for 51, the digital root works out to 6. 51: 3 all divide 51 evenly, out of 2-12. 51 is 110011 in binary and 33 in hex; as a Roman numeral it's LI.