I hope I don't steal words from future MikeMirzayanov's blog about 2021))
There were 142 contests (rated and unrated) in 2021. How many users participated in every of them?
The smallest number of participants is 31. It is VK Cup 2021 - Final (Engine). The greatest number is 19332 at Codeforces Round 697 (Div. 3). This numbers are got by API and include all official participants. But not all of participants were marked as “trusted participants” so there are usually less users shown in the contest final standings. Stats lovers can get more info from the interactive dashboard. Hover the mouse over columns to show info.
You can find interactive stat here. It contains data from the beginning of codeforces (+number of registrants)