Using "a Number of" as a Plural
Although the noun "number" is singular, the phrase "a number of plural noun" indicates that there are more than one thing concerned. Therefore, the verb that follows / precedes should never be singular.
- There are a number of people who have written about this subject.
- There is a number of students who have reported problems with the software.
- A number of hurdles still have to be overcome.
- A number of hurdles still has to be overcome.