Estonian registrikood

What it covers

Returns a valid Estonian registrikood (Commercial Register code for a legal entity) with a correct two-pass mod-11 check digit. Set `invalid=true` for a registrikood with a deliberately wrong check digit.

How it’s calculated

The Estonian registrikood (business registry code) is an 8-digit number whose final digit is a two-pass ISO 7064-style modulo-11 check digit computed over the first seven digits.

Payload digits: d1=1, d2=2, d3=3, d4=4, d5=5, d6=6, d7=7.
First pass with weights1 = [1,2,3,4,5,6,7]: 1*1 + 2*2 + 3*3 + 4*4 + 5*5 + 6*6 + 7*7 = 1 + 4 + 9 + 16 + 25 + 36 + 49 = 140.
r1 = 140 mod 11 = 140 - 132 = 8.
8 is less than 10, so the check digit is 8. The second pass is not needed.
Full registrikood: 12345678.

Edge cases

• When the first-pass residue r1 equals 10, the check digit is not simply 10 (which is not a single digit); a second weighted pass with weights [3,4,5,6,7,8,9] is run instead, and if that residue is also 10 the check digit falls back to 0. This mirrors the ISO 7064 two-pass fallback used by Estonia and Lithuania.
• The leading digit d1 encodes the entity type: 1 = commercial company, 7 = state institution, 8 = non-profit association, 9 = foundation. The generator only draws d1 from {1,7,8,9}, but the check-digit math treats d1 as a plain digit with weight 1.

Gotchas

• The weights are the plain ascending sequences 1..7 (first pass) and 3..9 (second pass), NOT a repeating/cyclic Lithuanian-personal-code style pattern. This generator passes exactly weights1=[1,2,3,4,5,6,7] and weights2=[3,4,5,6,7,8,9].
• The check digit is the raw residue itself (a 'remainder' scheme), never an 11-complement. There is no 11-minus-sum step; only the two-pass overflow-at-10 fallback applies.