po

Po is the small word that catches everyone out. It goes immediately before the number, never before the noun: po tri pomoj, not tri po pomoj. Traditionally po is a preposition, so the noun after it takes no -n; many writers treat it as an adverb-like word and add the -n when the phrase is an object (po tri pomojn). PMEG calls both correct. This site writes it without; pick one and be consistent. The related adverb pope means each or apiece on its own, and po never means the same as da, which measures a quantity rather than distributing it.