Properly Validate Credit Card Numbers

To make sure a credit card number is a valid card number, there is a relatively basic math process to apply. Starting from the end, if the positin of the digit is odd, you add its value to 2 times the digit that precedes it. If the position of the digit is even, you add double its value to the number that follows it. The resulting value should be a multiple of 10, which can easily be checked by using the MOD() function, expecting a result of zero.