Pill Prescription is the 21th puzzle from The Curious Village.
A man has been prescribed 10 pills. Starting today, he must take one pill a day, but because the concentration of the medicine is different in each pill, he must take them in a specific order. Since the pills all look the same, the man has decided to write numbers on each pill to help him remember the order he needs to take them in. How many pills does he have to number if he wants to keep track or the order?