"Two hundred forty five are on the table."

Translation: Două sute patruzeci și cinci sunt pe masă.

[RayVos]

I thought "masă" was the non articulated version. Since the sentence reads on "the table" shouldn't masă become "masa"? - which is what I wrote.

[Sollihein]

I am having the same difficulty with prepositions and usage of indefinite nouns after, when the English translation asks for definite ones. I cannot wait to get to that chapter to make sense of it.