If you’ve ever read the eight-digit serial number on a dollar bill, it was probably to play liar’s poker—or out of sheer boredom. But those digits are more than a passing diversion to a thriving online community, for whom they can take on a near-mystical significance.

At CoolSerialNumbers.com, Nashville musician and currency collector Dave Undis brings together like-minded digit-heads who have little interest in the history of money or even the denomination of a given note. Instead they are after certain patterns and series that fall under the flexible heading of “fancy” serial numbers.

Low serial numbers, from 00000001 to 00000100, are sought after, as well as palindromes (23599532), solids (with a digit that repeats eight times), seven-of-a-kinds (66666665), ladders (45678901) and important dates (12071941). The criteria get even more obscure from there: Undis is seeking a pi note, with the number 31415927. But the more apparently jumbled the digits, the less likely it is that anyone with the bill in their wallet will ever notice.

Which is too bad when you consider how much these fancy numbers can sell for—quite a bit more than the bill’s face value, in some cases. Right now, on Undis’ website, you can buy a $1 bill with the serial number 00000002 for a whopping $2,500. If that sounds like chump change, consider that a $5 bill with the number 33333333 goes for $13,000.

You can also peruse the Cool Serial Numbers collection, displayed via Google+, and get a sense for how oddly soothing a row of zeros can be, although “radar repeaters” have an interesting effect of their own, and who could resist collecting the elegant numbers of the Fibonacci sequence?

For all their fine specimens, however, Undis and his website are always on the lookout for new and fancier ones and have made available a comprehensive list of “Wanted” numbers, with any owners encouraged to get in touch about a sale or trade.

So the next time you’re about to pay the bartender or grocery store clerk, take a minute to examine your cash. You might be a lot richer than you realized.

H/T Boston.com | Photo by 401(K) 2012/Flickr