Number words - an exception
One strange exception to the rule given at Number words is the word number itself. We say "A number of points have been made", not "
has been made", and "A number of people were present", not " was" - although the Subject of the verb is singular - "a number" - in both cases. Another exception that feels perfectly idiomatic to a native is "The staff were also responsible for ... " where a logical user of the language might prefer "The staff was responsible".
Numeral words like million and hundred are followed by a singular in modern English. Say three million or five hundred, even if you think - rightly - that logically it should be
three millions and five hundreds. Human language is often not logical. (In older English, you will sometimes see these words used in their plural forms.)