po

Po is the small word that catches everyone out. It goes immediately before the number, never before the noun: po tri pomojn, not tri po pomojn. Zamenhof used it with the accusative when the whole phrase was an object, and that is still the standard, though you will meet writers who drop the -n after po on the argument that a preposition should not take one. Both are defensible; 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.