Suppose a magical wizard makes all man-made objects vanish and restores Earth to its prehistorical, stone age 20,000 BC state. What’s left are billions of naked humans, standing on grassy plains, in forests, in swamps, on tundra, and in deserts in the exact spots where their cities and villages were just a second ago. All fossil fuels will be replenished and will be in the same places and quantities as they were in 20,000 BC.
The humans themselves are unchanged. They're the same physical condition and age, and each person knows everything they know right now.
The wizard also leaves this message behind for every person in his/her language:
“I’ve cast a spell on all of humanity as an experiment. Here’s how it works: everything will remain as is until someone manages to discover a new million-digit prime number. Proof is required, so random guesses aren't allowed. Once that prime number is found, you have the option of reversing the spell and getting back all the man-made objects you had in 2018."
So the question is, how would this play out, and what’s your estimate for how long it would take for humanity to find that prime number? There would be mass casualties during the first few days and weeks, but could humanity rebuild civilization from scratch within a few decades? What about a few centuries?