How?
30 in Stockholm, population of ~950,000 21 in Boston, population of ~650,000 7 in Denver, population of ~700,000 etc...
I was going off of government info [0] but if you manually check you'll find it still works out albeit unicorns change pretty often at the moment.
[0] https://start.stockholm/en/about-the-city-of-stockholm/how-t...
edit: Okay Boston might have 31 [1], but while you're comparing leading cities to Stockholm you still have the remainder of the US which brings innovation rankings down. My overall point that Sweden has a decent level of innovation & startups (per capita) while maintaining a much better standard of living still stands IMO.
[1] https://www.crunchbase.com/hub/greater-boston-area-unicorn-s...