73 is a prime number.
To understand why, we need to look at the definitions of prime and composite numbers. A prime number is a natural number greater than 1 that cannot be formed by multiplying two smaller natural numbers. In other words, a prime number has exactly two distinct positive divisors: 1 and itself.
In the case of 73, the only divisors are 1 and 73. It cannot be divided evenly by any other number. For example, attempting to divide 73 by 2, 3, 4, or any number up to 8 (since the square root of 73 is approximately 8.5) shows that none of these divisions produce a whole number.
Thus, since 73 has no divisors other than 1 and itself, it is classified as a prime number.