With the introduction of SEPA, the use of IBAN is now mandatory for all bank transactions in the Euro zone. This forces almost everyone to migrate their data, replacing national bank account numbers with IBANs. Fortunately this is a fairly simple task: to get the IBAN for an existing account, take the two-character country code, add two check digits, and then the national bank account number you already have. But how do you compute the check digits?
