Is the word eight a noun in the sentence eight fat penguins?

In the phrase, 'eight fat penguins', the Word eight is an adjective used to define the number of penguins. The number eight is a noun when it is used as a number, for example, 'the apartment is number eight', 'the eight of clubs', or 'eight plus two equals ten'.

Please note that 'eight fat penguins' is not a sentence, there is no verb included.