Hungarian adószám

What it covers

Returns a valid Hungarian adószám (company tax number) with a correct törzsszám check digit. Use `format` for the full national number or the HU VAT form. Set `invalid=true` for a number with a deliberately wrong check digit.

How it’s calculated

The Hungarian adószám (VAT/tax number) carries a weighted modulo-10 check digit on the 8-digit törzsszám: the eighth digit is the 10-complement of the weighted sum of the first seven digits (weights 9,7,3,1,9,7,3) taken modulo 10.

Base digits: d1=1, d2=2, d3=3, d4=4, d5=5, d6=6, d7=7; weights [9,7,3,1,9,7,3].
Products: 1*9=9, 2*7=14, 3*3=9, 4*1=4, 5*9=45, 6*7=42, 7*3=21.
Sum S = 9 + 14 + 9 + 4 + 45 + 42 + 21 = 144.
r = 144 mod 10 = 4.
check = (10 - 4) mod 10 = 6.

Edge cases

• The check digit is fully determined by the first seven digits, so the eighth digit is never independently drawn — the generator computes it and appends it directly.
• The outer 'mod 10' in (10 - r) mod 10 matters only when r = 0: it maps the 10-complement of 10 back to 0, keeping the check digit a single digit.

Gotchas

• Only the first seven digits plus check digit (the törzsszám) participate in the checksum. The VAT code (Y, 1-5) and county code (ZZ, 02-20/02-44) are appended afterward and are NOT covered by any check digit.
• The weight vector is applied left-to-right starting at the first base digit (weight 9); it is not reversed and there is no separate weight for the check position (validation is done by recomputing from the seven base digits, not by a zero-sum-including-check form).