"31 million answers compared to 11 million" or 11 millions?

Question

I read on https://meta.stackexchange.com/q/361097/178179:

[Stack Overflow has] more than 31 million answers, compared to 11 million for the rest of the network.

Should million be in plural of singular form? I don't know what the correct rule is here since "answers" implicitly follows million.

Answer 1

1. The word million can be used as a noun or an adjective in English. million

2. In your example "million" is an adjective.

3. We don't pluralise adjectives

Let us substitute a different adjective. We will substitute "good" for "million".

[Stack Overflow has] more than 31 good answers, compared to 11 good for the rest of the network.

"11 good" is an abbreviation for "11 good answers".