When you sign up Hashnode shows you a list of 39 developers relevant for you to follow. If you hit the follow all button, you would follow 39 people. I hope this resolves the mystery. :)
I must be among the 39 as I see this, too. Is there an algorithm that chooses 39 as a specific number, then selects among communities? Or is it just 39 as a hard-coded value and there's 39 of us that have obscene amounts of followers? Just asking. :)