I understand that it's common to spell small numbers in words. However, all examples of this rule I could find use cardinals (i.e. expressing the size of a set of entities) like in:
- We met two cats and seven dogs.
- She has been driving for six hours.
My question is to what degree does this rule apply when one writes numbers as nouns rather than numerals? That is, which is the most 'correct':
- He chose the number 2.
- He chose the number two.
- He chose the number 'two'.