# I know I should know this... possible combinations?

Thru-Hiker
Thru-Hiker
My brain keeps telling me I should know how to do this, but I'm drawing a blank...

Looking at serial numbers all day. The first 6 number/letters never change, only the last three change. Either 0-9 or A-Z, and any combination of. xxxxxx09c, xxxxxx7u2, xxxxxx981, xxxxxx5tg, etc.

So how many possible combinations does that allow? More importantly, how is it figured? My brain wants to know.

Penguin
Penguin
You have 26 letters and 10 possible digits for each position in the serial number so that gives you 36 possible choices for each position assuming they can repeat. So there are 36 x 36 x 36 = 46,656 possible combinations. If instead they couldn't repeat you would have 36 x 35 x 34 = 42,840 possible combinations since each digit in the serial number would be eliminating a possible option.

It's been a little while but I'm confident enough this is correct.

Ken Newell
Ken Newell
Most manufacturers eliminate similar numbers and letters. Things like o and 0 or l, I, and 1. That may cut down the total a little bit.

Robin Bobcat
Robin Bobcat
Sometimes there will be gaps, as one of the codes is actually a timestamp, though with such a small number, it's unlikely. If you see something like "03197" followed by "04001", "04002", "04003" then you have a timestamp, with the first two numbers being 'when' (year, month, week, depending on application) and the rest being the order number within that time period.

Since you have some alphanumerics, then you're dealing with high-level serial number silliness. Stuff that requires more math than just 'add one to the last one we made' means they've got a REASON to have to convert to the letters.

This means one of two things: either they have a HUGE volume of production, and having the numbers stretching out for miles is undesirable (shorter codes are easier to enter into a computer, for example) - OR they want to purposely obfuscate the serial number. Again, one of two things: they want to keep just how many units are produced a secret, or they want to make sure someone isn't using someone else's number for, say, product registration.

Silound
Silound
My brain keeps telling me I should know how to do this, but I'm drawing a blank...

Looking at serial numbers all day. The first 6 number/letters never change, only the last three change. Either 0-9 or A-Z, and any combination of. xxxxxx09c, xxxxxx7u2, xxxxxx981, xxxxxx5tg, etc.

So how many possible combinations does that allow? More importantly, how is it figured? My brain wants to know.

Let me offer a warning about serials: No company does them the same, and unless you know for a fact they designate in a linear fashion (ie: xxxxxx001, xxxxxx002, xxxxxx003, ..., xxxxxxZZZ), there's no way to decipher them, or even know how many could actually exist.

Some utilize a letter to designate models or features (ever decipher the VIN on a car?). Some utilize time stamps. Some utilize crypto-based random seeds (GUIDS). Some simply do not use certain letters or numbers as someone else has pointed out.

Your absolute top end of unique serials would be 42,840 unique permutations using all 36 characters.

Your low end could range from 1 to 42,840

Snowtroll
Snowtroll
HP usually embeds a code for production site and week of manufacture in the serials of some types of equipment.

Then there's checksums...

J. Cook
J. Cook
Pretty much every printer they've ever made, and most of their pre-Cmopq computer gear was serialed in the same manner- the first two characters in the serial # are generally the country code where it was made.