The first 25 prime numbers (all the prime numbers less than 100) are: 2, 3, 5, 7, 11, 13, 17, 19, 23, 29, 31, 37, 41, 43, 47, 53, 59, 61, 67, 71, 73, 79, 83, 89, 97 (sequence A000040 in the OEIS).
Since a quantity is a variable that could be described in terms of numbers, then the quantities that can be measured exactly be integers would be, say, the amount of houses to be supplied with power and the number of people in the household. A fraction could never be a possible amount, because a person and a house is counted as one whole.
