It's just x % 7.
They started their example pattern with an citation number 984,946,606 they earlier said wasn't valid rather than 984,946,605 given initially (and shown in the image).
They started their example pattern with an citation number 984,946,606 they earlier said wasn't valid rather than 984,946,605 given initially (and shown in the image).
Check digits in your userdata is an old trick and is very useful in practice. Maybe modern systems should aim for something better than %7 but it's a good starting point as a system design concept.
> I was looking at ticket 984,946,605. When I type in 1 higher, 984,946,606, no ticket is found. ... So the ticket after 984,946,606 is actually 984,946,610