A £5 note has attracted bids of over £10,000 on eBay, thanks to its serial number.
The note is numbered AA01 444444 and has had 59 bids so far, from 16 people. And with two days to go before the auction closes, the top bid currently stands at £10,100.
Collectors are keen to snap up notes with low serial numbers, especially when they're new and in perfect condition. The lowest of all - AA01 000001 - has been presented to the Queen, but others have made tidy sums.
Cheeky eBay sellers asking thousands for 'upside down' £5 notes
At a Bank of England charity auction last year, a note numbered AA01 000017 sold for £4,150. And while the fiver currently on eBay has a higher serial number, the run of '4's makes it particularly eye-catching.
However, it remains to be seen whether the winning bidder will actually hand over the cash. Last October, a note with a series number starting AK47 made headlines when it attracted a bid of over £80,000 - but the buyer never paid up.
The £5 note that could be worth £1,000
More than a thousand £5 notes appear to have sold on eBay for sums of £200 or more since the new notes were released. Meanwhile the MoneySavingExpert website reports that some of its readers have sold AK47 notes for £35 or more.
"Although a banknote with the prefix AA01 might be worth slightly over face value to someone who is genuinely interested, we must remember that one million AA01 banknotes were printed," says Yasmin Britton of the Change Checker website.
"So as much as I wish it could be true, reality check – don't expect a big payout if you do find one."
According to Change Checker, it's not generally the serial number that attracts collectors - it's the name of the chief cashier. Some stay in the job for only a few years, making notes with their signatures rarer.
Elderly woman finds the third lucky £5 note - and gives it away
And there is one £5 note still out there that's more or less guaranteed to be worth thousands of pounds - the one remaining 'Jane Austen' note. When the new £5 was launched, micro-engraver Graham Short created tiny portraits of Jane Austen on four notes, along with a quote from the writer.
They are just visible to the naked eye, next to the image of Big Ben - and only three of the four have been found so far. The notes have an insurance value of £50,000 each - so it's very much worth looking out for the last one, which is numbered AM32885554.