An application that tests explicitly 16 digit credit card numbers against the Luhn Algorithm
I was bored and was searching out random things to code, came across a YouTube video from Half As Interesting about Decoding Credit Card Numbers
I later when looking for a number that would validate against both the Luhn Algorithm with and without the check digit found an infographic at 101Computing.net
I started to write in the logic for "Decoding" the card as mentioned in the video and stopped there for now.