LuhnProduct is the last of the three Luhn functions and the result is checked by Luhn to see if it is divisible by 10 without any remainder. If it is then the number is valid. By valid we mean it is correctly formatted - this has nothing to do with available credit.
As a stand alone function it adds together each digit in a number.
LuhnProduct (doubleEven)
/*
A component of the Luhn function.
Add all the numbers together
*/
If ( Length ( doubleEven ) > 0 ;
Middle(doubleEven ; 1; 1) + Middle(doubleEven ; 2; 1) + LuhnProduct ( Right ( doubleEven ; Length ( doubleEven ) - 2 ) )
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