The difference between set of whole numbers and a set of integers is that:
Whole numbers = {0, 1, 2, 3, 4, 5...}
Integers = {..., -5, -4, -3, -2, -1, 0, 1, 2, 3, 4, 5...}
If we name contents of the first set as n, in the second set you can have 2n-1 numbers (because we count 0 only once in both sets).