a number of 意思是“许多...”,后接复数名词,谓语通常用复数：
A number of students were absent from the meeting.
许多学生没有到会.
the number of 意思是“.的总数”,后接复数名词,但谓语要用单数：
The number of students absent from the meeting was surprising.
没有到会的学生人数很惊人.
所以由上可知,两者之后都可加复数名词,但谓语动词用法不一样!
a number of 的用法