Learn Dutch: Ik had er drie blauwe bemachtigd, zonder de hoes. - I had acquired three blue ones, without the sleeve.

Here, er acts as a quantitative pronoun, meaning "of them". Because the actual noun (like records or shirts) is omitted and only the number (drie) is mentioned, Dutch requires you to use er to refer back to the missing items.

Why does blauwe have an -e at the end?

When an adjective is used as a noun to mean "blue ones", it almost always takes an -e ending. It behaves just like a regular adjective modifying a noun, but the noun itself has been dropped because it is clear from context.

Is bemachtigen just a synonym for krijgen (to get)?

Not exactly. While krijgen is the standard word for "to get" or "to receive", bemachtigen implies that it took effort, skill, or luck to obtain the items. It translates better to "to get hold of", "to secure", or "to score" (like a rare vinyl record).

Why does the past participle bemachtigd come before the phrase zonder de hoes?

While Dutch normally puts the past participle at the very end of the clause, prepositional phrases like zonder de hoes can often be placed after the final verbs. This is a common exception that makes the sentence flow better and prevents a "traffic jam" of words before the verb.