The set of counting numbers between 20 and 28 is: 21, 22, 23, 24, 25, 26, 27.
Counting numbers, also known as natural numbers, start from 1 and go up indefinitely. When we refer to the counting numbers between two values, we consider only the numbers that lie strictly between those two values, excluding the endpoints. In this case, we exclude 20 and 28 and include all whole numbers that come after 20 up to 28, but not including 28 itself.