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Number to check

Luhn check digit calculator

PAN without check digit

</> Code Implementation

# Luhn Algorithm — validate and generate check digit
# No external dependencies required

def luhn_validate(number: str) -> bool:
    digits = [int(c) for c in number if c.isdigit()]
    total = 0
    for i, d in enumerate(reversed(digits)):
        if i % 2 == 1:
            d *= 2
            if d > 9:
                d -= 9
        total += d
    return total % 10 == 0

def luhn_check_digit(partial: str) -> int:
    for check in range(10):
        if luhn_validate(partial + str(check)):
            return check
    return -1

# Example
pan = "411111111111111"
check = luhn_check_digit(pan)
full  = pan + str(check)
print(f"Check digit : {check}")
print(f"Full PAN    : {full}")
print(f"Valid       : {luhn_validate(full)}")
# Check digit : 1
# Full PAN    : 4111111111111111
# Valid       : True