Classify numbers | Algebra (practice) | Khan Academy Practice classifying numbers as whole, integer, rational, and irrational. If you're seeing this message, it means we're having trouble loading external resources on our website. If you're behind a web filter, please make sure that the domains *atic and *ndbox are unblocked.Classifying Numbers · Worked Example Sets of numbers - Free Math Worksheets The set of natural numbers is often referred to as the set of counting numbers, because they are those numbers that we use to count. Notice the three dots in the set notation. That means that the set continues without end. Also notice that 0 is not included in the natural numbers.