Pizza Shack promotes a special lifetime offer--once you order all possible pizza combinations from Pizza Shack , you can get free pizza for life! Pizza Shack offers a selection of 13 toppings...

Pizza Shack promotes a special lifetime offer--once you order all possible pizza

combinations from Pizza Shack , you can get free pizza for life! Pizza Shack offers a

selection of 13 toppings (including cheese) for their pizzas. How many different pizzas

must you order from Pizza Shack to qualify for their lifetime offer? Is this possible?

Explain your reasoning.