Find a banknote with a ‘solid’ serial number? It’s probably worth so much more

(NEXSTAR) – Building a collection of unique banknotes? You'd be off to a solid start if you find one with a "solid" serial number.

A "solid" serial number, as known to collectors, is a serial number on a U.S. banknote that features only a single repeating digit, such as "11111111" or "77777777." Bills with such numbers might not be quite as rare as, say, a discontinued banknote or a bill with a double denomination error, but they're still among some of the most recognized "oddities" in paper-money collecting, according to Doug Mudd, the curator and director of the American Numismatics Association's Edward C. Rochette Money Museum in Colorado.

"As a type, they are somewhat popular because they are more readily noticeable," Mudd tells Nexstar.

Mudd pointed out, however, that a "solid" serial number is technically "just as rare or common as any other," mathematically speaking. But much like collectors who seek out "radar" serial numbers (i.e., palindromic numbers, such as 12344321 or 55433455), there are indeed niche collectors willing to pay well over face value for more unique specimens.

In fact, banknotes with solid serial numbers generally fetch more than other so-called "fancy" serial numbers, seeing as there are fewer possible bills with solid numbers in a series.

"Many collectors don't have a solid among their fancy serial number notes," one member of Reddit's r/PaperMoney community remarked in a post about a collector who found a "solid" $20 banknote earlier this year.

"Right place, right time, I guess," the user said.

Archived auction data from Heritage Auctions and Stacks Bowers shows that solid-numbered bills have routinely sold for thousands of dollars apiece, if they're in good condition. Some buyers have also paid premiums for specific solid numbers like 77777777 or 88888888 — numbers thought to be more lucky or auspicious in certain cultures. (A "near-perfect" $100 bill with a solid 8 serial number sold for more than $19,000 in 2024, the Heritage Auction website indicates.)

Imperfect bills with solid serial numbers can still fetch many times their face value, recent eBay sales indicate. An ungraded $1 note with a solid 3 serial number sold for $1,600 earlier this month, while a $5 bill with a solid 2 serial number sold for $2,660 as part of a series with several other bills of sequential serial numbers. The auction platform also appears to be crawling with "near solid" or "almost solid" banknotes for sale (e.g., 44444447 or 91999999), though those were selling for far less.

Mudd, meanwhile, told Nexstar that bills with fancy serial numbers are generally less "interesting" to most paper-money hobbyists or historians, as they aren't exactly anomalies, and don't come with much of a story. But when it comes sheer value, these bills certainly have their buyers.

"[They're] definitely worthwhile to the specialist," Mudd said. "[…] There are people very interested in them and they will pay more money."