Ugly Numbers

Definition : 

               

                  The number whose only prime factor is 2,3 and 5 is known as a ugly number. 

1 is the smallest ugly number because - 

                                              1 = 2 the power 0 or  2⁰
                                              1 = 3 the power 0  or 3⁰
                                              1 = 5 the power 0  or 5⁰

1 is the smallest ugly number and it's base case.