Slovenian davčna številka

What it covers

Returns a valid Slovenian davčna številka (tax number for a person or company) with a correct check digit. Use `format=vat` for the SI VAT number. Set `invalid=true` for a tax number with a deliberately wrong check digit.

How it’s calculated

The Slovenian davčna številka appends one check digit to seven payload digits using a weighted sum modulo 11, taking the 11-complement — except residue 1 collapses to check digit 0 and residue 0 has no valid check digit (unissued prefix).

Payload digits: d1..d7 = 1,5,0,0,3,6,5
Weights: 8,7,6,5,4,3,2
Products: 1*8=8, 5*7=35, 0*6=0, 0*5=0, 3*4=12, 6*3=18, 5*2=10
Weighted sum = 8+35+0+0+12+18+10 = 83
Residue r = 83 mod 11 = 6 (11*7=77, 83-77=6)
r is neither 0 nor 1, so check = 11 - 6 = 5

Edge cases

• Residue r == 1 → check digit is 0 (the naive 11-complement of 10 is folded down to 0), not rejected.
• Residue r == 0 → NO valid check digit exists (11-complement would be 11); the generator treats this prefix as unissued and redraws seven new payload digits.
• The first payload digit d1 is always drawn 1-9 (never 0), matching the common shape of a real davčna številka.

Gotchas

• This is NOT the plain 11-complement used by some other IDs: the two special residues (0 and 1) are handled differently — 1 maps to 0, and 0 is invalid rather than mapped.
• The shared weightedSum primitive returns only the raw positional weighted sum; the mod-11, the complement, and both special-case rules are applied inline in computeDavcnaCheckDigit, not inside the primitive.
• The same davčna številka identifies both persons and companies; there is no sex or century marker in the number — all eight digits except the check are unstructured payload.