I do not known. But numbers can be nouns. If they are used as noun you have to know the right articel. But when I think about it they are all femal, so it doesn`t make sense. In colloquial language numbers are often used without articles.

In general numerals get the die article. The article is more useful for when it is in a sentence and you just need to know the gender to properly use it. So i consider it more for sentence grammar rather than actually saying 'the six' instead of 'six'.

Die Zahlen sind weiblich und Einzahl (Singular). Die Eins ist eine Zahl, die Zwei, die Drei und die Vier auch... Need more examples? ;-)

seventeen is just siebzehn. If you want to say "the 17" you mean "the (number) 17)" so it's "die siebzehn" as a special one.

Sometimes DL is a bit weird. Of course do we Germans count "eins, zwei, drei, ...". There is no way you will find one counting "die Eins, die Zwei, die Drei,...".

Leonie - I don't know why anyone would down-vote your answer. I up-voted and give you a Lingot.