Tools to check Luhn generated numbers. The Luhn algorithm (also called modulo 10 or mod 10) is a checksum formula for numbers/digits used with credit card or administrative numbers.

Luhn (Number checksum) - dCode

Tag(s) : Checksum,Algorithm,Arithmetics,Mathematics

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Tools to check Luhn generated numbers. The Luhn algorithm (also called modulo 10 or mod 10) is a checksum formula for numbers/digits used with credit card or administrative numbers.

This algorithm allows checking credit card numbers MasterCard/AMEX/Visa of IMEI codes for example by using a control key checksum. If one character is badly written, in the Luhn algorithm can detect it.

Let 12345674 be a valid card number, 1234567 is the main original number and 4 is the checksum.

If a user enter 13245674, then the program calculates the checksum for 1324567 and finds 5 instead of 4 expected, the number is invalid and so has been badly typed.

The algorithm starts by the end of the number, from the last right digit to the first left digit. One realises a sum of digits by multiplying by 2 all digits of even rank. If the double is equal or superior to 10, one replaces it by the sum of its digits. The control digit number is equal to (10-sum%10) % 10.

Let the number be 853X, with X=0, the digit we want to calculate.

One takes the digit 3, doubled, 3*2 = 6,

One takes the digits 5, not multiplied by 2

And one takes the 8, mutiplies it by 2 : 8*2=16 and 1+6=7 to get 7.

The sum is 6+5+7 = 18. As 18 modulo 10 = 8, one calculated (10 - 8) %10 = 2, 2 is the digit checksum control.

So 8532 is valid.

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