Most people know the saying, “A dollar saved is a dollar earned.” But did you know some $1 bills are actually worth hundreds—or even thousands—of dollars? While coins often get attention from collectors, paper currency with unusual serial numbers can be just as valuable.

Every U.S. dollar bill carries an eight-digit serial number. Most are ordinary, but rare patterns stand out to collectors. Because the Bureau of Engraving & Printing sometimes removes unusual sequences, those that slip through become highly prized.

One of the most sought-after patterns is the ladder, where numbers run in perfect order, such as 01234567. Radar notes are also popular, with numbers that read the same backward and forward, like 22211222.

Even rarer are super radars, where the middle six digits match, such as 23333332. Collectors also chase repeaters, where a sequence repeats (01570157), or super repeaters, which use only two digits in alternating order, like 01010101.

More complex combinations include the radar repeater (12211221) and the double quad, where two sets of four matching digits appear, like 00003333.

Other valuable finds are bills with seven in a row (11111115) or seven of a kind scattered across the number (11115111). Finally, there are binary notes, which use only two digits, such as 11313111.

Before spending your cash, take a closer look at the bills in your wallet. Spotting one of these rare patterns could mean you’re holding a valuable collector’s item rather than just pocket change.

Websites like coolserialnumbers.com can help estimate the potential value of unusual bills. Even if you don’t find one, collecting currency can be a fascinating hobby—and a reminder that sometimes money is worth more than its face value.