Miranda, *As a general rule "a number of" means more than one and requires a plural verb. -There are a number of italki users online right now........correct. By contrast "the number of" takes a singular verb because the definite article "the" emphasizes the word 'number' as a single unit. -There is the number of italki users in China, for example. -The number of italki users is large. When "a number of" is used with an adjective it often takes the singular verb because the adjective also emphasizes the singularity of the word 'number'. -There's a large number of people outside. -There is an increasing number of italki users. *There is nothing wrong with using a singular verb with " a number of" if you are emphasizing 'number' as a unit but it is rarely used that way. A number of people is online.......Okay, but not common.

There are. A number of modifies plural forms of count nouns, so we only say' there are a number of...'. For example There are a number of birds in the tree. There are a number of people on the street on weekends.

"There is". There's a large number of people outside. There are large numbers of people in every Chinese city. OK?