Let's perform the operation on the first input code:
371449635398431
every other digit (starting from second-to-last)
3 8 3 3 9 4 7
doubled and summed up
6 + 16 + 6 + 6 + 18 + 8 + 14 = 74
remaining digits (starting from the left), summed up
3 + 1 + 4 + 6 + 5 + 9 + 4 + 1 = 33
Total = 107
So, at least I can confirm that, according to the rules depicted, the first input code should be rejected.
Either we're right (and the 'solution site' is wrong) or we're wrong (bad computation) or the reported rules are miswritten (or misunderstood).
[update]
According to this site
Credit Card Number Generator & Validator - FreeFormatter.com[
^] such input is a valid credit card number. However the rules followed are a bit different, namely they follow the
Luhn
algorithm. Since the algorithm is well described in the same site, I suggest you to have a look at it.
[/update]