You arrive at the party and the host personally comes out to greet you. He invites you in to the party and takes you to his office.
What madness is this!?!?
He gives you a numbered list of ingredients for his famous meatball recepie, and tells you that some of the ingredients are red herrings (but none of them are red herring). He has encoded the numbers of the correct ingredients; you have to figure out how to decode them into the proper numbers. He gives you some examples: "6" decoded is "20", "2" decoded is "4", and "3" decoded is "8".
Your friend has given up. He says good bye and leaves. The host tells you that the correct ingredients are those with numbers decoded from "1", "7", "10", and "9". What ingredient numbers are correct?
By the way, if you get this wrong a trampling elephant is waiting!