Last year 666777.com went for $65,500 at GoDaddy auctions. One year later the price is almost $50,000 off. The domain name expired and closed at $16,750.
This is the continuing decline of numeric domain names as it seems the interest from China is just not there.
147.com sold at Sedo for the lowest reported NNN.com price in 7 years a couple weeks ago.
509.com sold for $275,000 in 2018 and went for just $106,000 in February.