Thank you, JulianStuart. I couldn't find those threads when I searched for my phrase.
number of is are - WordReference.com Dictionary of English Usage
2. As a collective noun, number, when preceded by a, is most often treated as a plural:A number of legislators have voiced their dissent.When preceded by the, it is usually used as a singular:The number of legislators present was small.
It says "most often". When is it NOT treated as a plural? Could anyone give me some examples?