I was also intrigued, so I searched and on wikipedia ( https://en.wikipedia.org/wiki/International_Bank_Account_Number https://en.wikipedia.org/wiki/Internation

I was also intrigued, so I searched and on wikipedia ( https://en.wikipedia.org/wiki/International_Bank_Account_Number https://en.wikipedia.org/wiki/International_Bank_Account_Num... ), in the section "Validating the IBAN" it is written : Interpret the string as a decimal integer and compute the remainder of that number on division by 97 If the remainder is 1, the check digit test is passed and the IBAN might be valid