There is confusion here.You're a raging moron if you think "an" is an adjective.
It's an article, trust me.
I said it was an adjective. Oxford says so. Oxford rules for English as L'Académie française rules for French, Cervantez for Spanish and Dante for Italian.
LRS, in all fairness, said it was more like an article. He's right if you rely on Webster, which is okay, it's American and colloquial. But okay.