Numbers / 400

The Number 400

400 is composite: factorization 2^4 × 5^2. That gives 400 exactly 15 divisors: 1, 2, 4, 5, 8, 10, 16, 20, 25, 40, 50, 80, 100, 200, 400. 400's proper divisors total 561, 161 more than 400 itself, so 400 is abundant. 400 is also a perfect square, since 20² = 400. 400 has a digit sum of 4; for 400, the digital root works out to 4. 400: 2, 4, 5, 8, 10 all divide 400 evenly, out of 2-12. 400 is 110010000 in binary and 190 in hex; as a Roman numeral it's CD.