I once heard of that the article "the" can be omitted after "of".
So which sentence should I choose,
"in terms of the number of something" or "in terms of number of something"?
At the same time, I know that it's incorrect to say
"an expression for number of something".
It have to be
"an expression for the number of something".
For example,
"We derive an expression for the number of the mean value".
What's the difference between "the" after "of" and after "for"? Why?