The coins proposed are all prime, which makes sense to me intuitively. You'll always need a 1 coin. I'm curious if it's generally true that optimal coins for any given range starting at 0 will be primes?
I take issue with the assumption that you always need a 1 coin.
If we're going to go to such great lengths to minimize the number of coins, even at the cost of making real-life transactions more complicated, we could totally forgo the 1 coin and just have 2 and 5. If an amount ends in 1, you pay 5 and get two 2s back. Now you can have a coin system that is entirely primes!
