Selenium IDE: Get random object from an array

Okay, I know there have been lots of similar questions to this one asked but the answers are not helping me since it is a Selenium IDE question.

Using Selenium IDE, I am trying to get a random test credit card number from an array and I want it to pull a random CC# from the list every time the test gets run. Below is my code. As of now it just outputs NaN.ANy ideas? Thanks!

RandomCC generator