Calculator trick

Nope. In fact, quite the opposite. The trick was all in the setup before he had Penn enter the first number. This is actually a rather dumb trick that you can easily perform on other people. If you want to learn how, read on:

Choose a large number, such as Ben's 577,345,993 (Actually, his number was a dumb choice because it ends with an odd number, and only made it obvious that the final answer wasn't actually the product of the three numbers that Penn, Teller, and Allyson chose--any even number times anything is always an even number as the previous poster alluded to--but he wanted it to spell "eggshells" in the end).

In your (or someone else') calculator app, enter your chosen number, then press the plus symbol (+), followed by zero (0), followed by the multiply button (×). This will leave a "0" in the display as if the app had just been opened. You can even minimize the app as long as you don't close it. You could also hand the phone to someone else and let them do all the calculations from this point forward. The previous operations will be waiting for someone to input the next number, then the multiply button again, and another number, etc., before finally pressing the equal sign. No matter how many numbers they input, they are being multiplied by zero and then being added to the very first number you entered, so that's the number that will result.

The "Toxic" that Teller had hidden upside-down in his written message to Ben is simply the mnemonic to remember tox (+0×).

Revenge is a dish best served with barbeque sauce.