FA-72598 / Check-digit algorithms / Member archive

Second control digit uses the supplied first control digit · case 03

When the first control digit is mistyped, the reported expected second control digit is also wrong.

Member previewVariant 3 · 3 implementations · 8 checks per implementation

Case contract

Norwegian-style 11-digit national identity number with two mod-11 control digits. k1 uses weights 3,7,6,1,8,9,4,5,2 on digits 1-9; k2 uses 5,4,3,2,7,6,5,4,3,2 on digits 1-9 followed by the computed k1. Each is 11 - (sum mod 11) with 11 mapped to 0; a value of 10 means the base number is "unassignable". Non-11-digit input is "malformed". Return [k1, k2, whether digits 10 and 11 equal k1 and k2].

Why this case matters

Population registers validate national identity numbers and report which control digit disagrees.

One recorded failure

Sample boundary fixture

This sample comes from the broken implementation of a controlled reproducer.

Boundary fixture	Actual	Expected	Outcome
regression ["12060326049"]	`[0, 3, false]`	`[0, 0, false]`	Failed

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