

Ask HN: Why do parking tickets across lots of cities follow a similar # pattern? - davidhegarty

We noticed something interesting as we were looking at parking ticket numbers.<p>The sequence of parking ticket numbers follows a similar pattern across lots of different cities.<p>We thought it was because cities shared a similar software vendor... but it looks to be more extensive than that.<p>Anyone have any ideas why a large number of cities have the following parking ticket sequence:<p>827778501	 (+11)
827778512	 (+11)
827778523	 (+11)
827778534	 (+11)
827778545	 (+11)
827778556	 (+11)
827778560	 (+4)<p>...and then continues to add &#x27;11&#x27; six times, and then adds a &#x27;4&#x27;, and keeps repeating.<p>Is there a reason for this?
Is it a common sequence in other places too?
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madcaptenor
The last digit may be a check digit. In particular, it might be the remainder
upon dividing the number that the other digits make by 7. For example 82777850
divided by 7 leaves a remainder of 1. Some examples of this check digit
scheme:

[http://nrich.maths.org/2036](http://nrich.maths.org/2036)
[http://www.cbp.gov/sites/default/files/documents/in_bond_che...](http://www.cbp.gov/sites/default/files/documents/in_bond_check_1.pdf)
(with a clunky implementation) [http://www.con-
way.com/en/tools_pricing/freight/fr_tools/tra...](http://www.con-
way.com/en/tools_pricing/freight/fr_tools/tracking/pro_number_check_digit_formula)

~~~
davidhegarty
BINGO!!! You da man. That's seems to work for all my examples.

Thanks!

