Credit card numbers follow certain patterns. A credit card number must have between 13 and 16 digits. It must start with:
- 4 for Visa cards
- 5 for Master cards
- 37 for American Express cards
- 6 for Discover cards
In 1954, Hans Luhn of IBM proposed an algorithm for validating credit card numbers. The algorithm is useful to determine whether a card number is entered correctly or whether a credit card is scanned correctly by a scanner. Credit card numbers are generated following this validity check, commonly known as the Luhn check or the Mod 10 check.
Here is a Java code to check the above.