Good point. Have two programs - one checking every even number and returning odd of not even. And then have a program checking every odd number and returning even if not. Then, a simple program to dispatch to either program randomly, so you end up in the long term with good performance for each.
Your mention of Microservices opened up my mind to additional possibilities. How about we create a microservice for each integer, then deploy 4 billion of them. Send a request to all of them simultaneously. Only one of them will respond with the answer. We still need to decide how to deploy those microservices - one per machine, or multiple per machine?
