Numbers / 4

The Number 4

4 is composite: factorization 2^2. That gives 4 exactly 3 divisors: 1, 2, 4. 4's proper divisors total just 3, 1 short of 4, the deficient case most of 4's neighbors share too. 4 is also a perfect square, since 2² = 4. 4 has a digit sum of 4; for 4, the digital root works out to 4. 4: 2 all divide 4 evenly, out of 2-12. 4 is 100 in binary and 4 in hex; as a Roman numeral it's IV.