Are numbers also functions in functional programming?

Question

I have been taught in my Bsc course that in functional programming even numbers are functions that return themselves. I've read that lambda calculus consists only of functions and nothing else, so that would make sense. However, I didn't find any articles about functional programming that introduced numbers as functions. However(!), I also read that expressions in functional programming are functions and numbers are considered expressions, thus numbers must be functions...right?

In short, I am very confused about what is and isn't a function in functional programming.