Hungarian TAJ

What it covers

Returns a valid Hungarian TAJ (társadalombiztosítási azonosító jel) with a correct mod-10 check digit. The TAJ is non-semantic — it encodes no birth date or sex. Set `invalid=true` for a deliberately wrong check digit.

How it’s calculated

The Hungarian TAJ (social-insurance number) check digit is the weighted sum of the first eight digits under alternating weights 3 and 7, taken directly modulo 10 (not a 10's-complement).

Payload digits: d1..d8 = 1,2,3,4,5,6,7,8
Weights: 3,7,3,7,3,7,3,7
Products: 3*1=3, 7*2=14, 3*3=9, 7*4=28, 3*5=15, 7*6=42, 3*7=21, 7*8=56
Sum = 3+14+9+28+15+42+21+56 = 188
Check digit = 188 mod 10 = 8 (taken directly as the remainder)

Edge cases

• Leading-zero TAJ: the first digit may be 0 (produced by the edge generator), so a numeric parse silently drops it to eight characters — TAJ must be kept as a string.
• Zero check digit: the ninth digit can legitimately be 0 when the weighted sum is a multiple of 10 (e.g. sum 188 gives 8, but sums like 190 would give 0), so a 'trailing digit is non-zero' assumption is wrong.
• Repeated-pattern payload: all eight payload digits identical still produces a valid TAJ, so 'looks like a placeholder' filters wrongly reject genuine values.

Gotchas

• The check digit is the raw remainder sum mod 10 — NOT 10 minus the remainder. Applying a 10's-complement (as many other national schemes use) yields the wrong digit.
• The weights alternate 3,7,3,7,3,7,3,7 across the eight payload digits; do not start with 7 or use a Luhn-style 2,1,2,1 pattern.
• The modulus is 10 despite the primitive living in mod11.ts — only the generic weightedSum helper is reused; the '% 10' and the 3/7 weights are supplied by the TAJ generator itself.