The number 28 is an even integer that follows 27 and precedes 29. It is known for being a perfect number, which means that the sum of its proper divisors (1, 2, 4, 7, and 14) equals the number itself. This property makes 28 unique in the study of numbers. However, 28 is not a prime number. A prime number is defined as a natural number greater than 1 that has no positive divisors other than 1 and itself. Since 28 can be divided evenly by numbers like 2, 4, 7, and 14, it does not meet the criteria for being prime.