twenty-seven vs xxvii

twenty-seven is a noun but xxvii is not a noun.

Word	Noun	Adjective	Verb	Adverb
twenty-seven	Yes	Yes	No	No
xxvii	No	Yes	No	No

As adjectives, twenty-seven and xxvii are synonyms defined as:

Other synonyms of twenty-seven include 27.

twenty-seven (noun)	xxvii (noun)
the cardinal number that is the sum of twenty-six and one

twenty-seven (adjective)	xxvii (adjective)
being seven more than twenty	being seven more than twenty