 This is defined by 3GPP2 standard X.S0008.The hexadecimal form is specified to be 14 digits grouped together and applies whether all digits are in the decimal range or whether some are in the range 'A'–'F'.In the first case, all digits are in the range '0'–'9', the check-digit is calculated using the normal base 10 Luhn algorithm, but if at least one digit is in the range 'A'–'F' this check digit algorithm uses base 16 arithmetic.