You have 10^15 possible values from a 16-digit CC number (due to Luhn's algorithm). The first 6 are for the issuer/bank; if you know that, you have 10^9 or abou

You have 10^15 possible values from a 16-digit CC number (due to Luhn's algorithm). The first 6 are for the issuer/bank; if you know that, you have 10^9 or about 30 bits of possible values.