get the admin username of a multisite blog

Hello

I use the function get_userdata (username) to get a variable file.
So eg the user (=admin and only user of a multisite blog) “test” would see the content of the file:
….com/folder/’.$username.’.txt = ….com/folder/test.txt

This works, though this is for a multisite and I would like the superadmin to see the same content…but of course the admin won’t see the same since wordpress then pulls the content of the file ….com/folder/superadmin.txt, which doesn’t exist.

So I would like a function that doesn’t get the username of the logged in user, but the username of the admin of the current blog, so the username sees the same content as the admin of the blog.

Is there such a function? If so, it would be great if you could show it.

Thanks in advance
Steven