Numbers / 45

The Number 45

45 is composite: factorization 3^2 × 5. That gives 45 exactly 6 divisors: 1, 3, 5, 9, 15, 45. 45's proper divisors total just 33, 12 short of 45, the deficient case most of 45's neighbors share too. 45 is also the 9th triangular number, the sum of 1 through 9. 45 has a digit sum of 9; for 45, the digital root works out to 9. 45: 3, 5, 9 all divide 45 evenly, out of 2-12. 45 is 101101 in binary and 2D in hex; as a Roman numeral it's XLV.