'Concrete numbers' are a type of phrase consisting of a number and a unit expressed with a noun, such as 'two metres', 'three apples' etc. Historically called numerus numeratus
Take '5 men', it does not definitely describe any group of men in existence, however it does indentify correctly the exact amount/particular measure type, a unique idea, Hence it may or may not denote a particular group of men depending on the context.
'5 men entered a bar, and played a game of darts'
This is therefore an indefinite description and follows the rules that it can describe something and denote it contextually.
However in some context it is treated as a phrase that unambiguously denotes the idea of amount of a certain type.
'The price is 5 dollars'
If '5 men' denoted the idea of that amount of men then it would be difficult to explain what an idea is doing entering a bar.
Why is it that these kind of phrases which seemingly is an indefinte description and describes (contextually it may denote the object being described) is seen as unambiguously denoting the abstract idea of the amount?
Using an indexical phrase like 'The Price' in 'The Price is 5 dollars' with something ('5 dollars') that is not a proper noun (or some other unambiguous denoting phrase) seems ungrammatical.