Numbers / 405

The Number 405

405 is composite: factorization 3^4 × 5. That gives 405 exactly 10 divisors: 1, 3, 5, 9, 15, 27, 45, 81, 135, 405. 405's proper divisors total just 321, 84 short of 405, the deficient case most of 405's neighbors share too. 405 has a digit sum of 9; for 405, the digital root works out to 9. 405: 3, 5, 9 all divide 405 evenly, out of 2-12. 405 is 110010101 in binary and 195 in hex; as a Roman numeral it's CDV.