Please don’t resurrect old threads, and make an MWE with your question as per this post.
It’s likely that you just re-bound mean (or silhouettes) to a number somewhere in your code:
julia> using Statistics
julia> mean = 5
5
julia> mean(rand(10))
ERROR: MethodError: objects of type Int64 are not callable
Matt’s code from the post above works just fine for me in a new session.