43 is a prime number.
A prime number is defined as a number that is greater than 1 and has no positive divisors other than 1 and itself. When we look at 43, we can see that it cannot be divided evenly by any other numbers except for 1 and 43. The only divisors of 43 are indeed 1 and 43, which confirms its status as a prime number.
In contrast, a composite number has more than two positive divisors. For example, the number 4 is composite because it can be divided by 1, 2, and 4. Since 43 does not meet this criterion, it is classified as prime.
In summary, 43 is a prime number because it only has two divisors: 1 and itself.