Checking company numbers in Sweden, Norway, Finland and France with check digits

Each of these four countries assigns companies a number that ends in a check digit, which lets forms catch many typos before a register lookup. Sweden uses a 10-digit organisationsnummer validated with Luhn, Norway a 9-digit organisasjonsnummer using a mod 11 weighting, Finland a 7-digit Y-tunnus with a mod 11 check, and France a 9-digit SIREN or 14-digit SIRET validated with Luhn. The article provides JavaScript validators for each format and notes that a mod 11 remainder of 10 means no valid number exists for that body. It also explains how VAT numbers can be derived from company numbers in Sweden, Finland, Norway and France, while cautioning that a derived VAT number does not confirm VAT registration. The author, who works on a company-check API, presents the code as usable without that service.