On some days several

"Let all the poisons that lurk in the mud hatch out”: the muttered incantation of the emperor in Robert Graves’s Claudius the God has rarely seemed so apposite. It is time for this government to drop the pretence that it is healthy and functioning. A reckoning is long past due. Daily, we see a new pustule or sore – on some days several. (The Guardian.)

Is "several" a postdeterminer or an adjective in the prepositional phrase "on some days several"?