IBAN Validator
How the checksum works
An IBAN's first 4 characters (country code + 2 check digits) are moved to the end, each letter is converted to two digits (A=10 … Z=35), and the resulting number must be congruent to 1 modulo 97 — the ISO 7064 "mod 97-10" check. That number is far too large for ordinary arithmetic, so it is reduced incrementally, one digit at a time, instead of ever being formed in full. A checksum pass means the IBAN is internally consistent; it does not confirm the account exists or belongs to anyone.
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