Whether the verb with “number of” expressions takes a plural
verb or a singular verb depends on the article used: "the" or "a."
But the expression a
number of (with the indefinite article “a”) has a plural meaning and
requires a plural verb.
The number of planes lined up for takeoff is the most I’ve ever seen.
A number of planes are lined up for takeoff.
The number of
protesters indicates dissatisfaction
with the proposed legislation.
A number of protesters have indicated their dissatisfaction with the proposed legislation.
Questions? You have my number!