FA-72528 / Check-digit algorithms / Member archive

ABA prefix range stops before 12 · case 03

Routing numbers with prefix 12 are reported malformed.

Member previewVariant 3 · 3 implementations · 8 checks per implementation

Case contract

US ABA routing transit number: exactly nine ASCII digits whose first two digits lie in 00-12, 21-32, 61-72 or equal 80 (else "malformed"). Weights 3,7,1 repeat from the left; return whether the weighted sum is a multiple of 10.

Why this case matters

ACH origination checks routing numbers before transmitting a batch.

One recorded failure

Sample boundary fixture

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

Boundary fixture	Actual	Expected	Outcome
regression ["121199382"]	`"malformed"`	`true`	Failed

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