Factors and Perfect Numbers
                    
                        Factors of a number N are numbers that are less
                        than or equal to the number N which, when some of them are multiplied
                        together, give the number N.
                        
                        Example: The factors of 6 are 1,2,3 and 6. When 2 and 3 are multiplied
                        together, they give 6 and so do 1 and 6 when multiplied together.
                        
                        
                        A Perfect Number is a number N whose factors that
                        are less than itself add to the same number N.
                        
                        Example: The factors of 6 are 1,2,3,6. The factors that are less
                        than 6 are 1,2 and 3. Adding 1 + 2 + 3 = 6. This makes 6 a perfect number.
                        
                        Very few perfect numbers exist, as can be verified here.