You find a mysterious note slipped under the school library door. It contains this sequence: 2, 4, 8, 16, ?, 64. Below it, another sequence: A, C, E, G, ?, K. And a third: 🔺🔵🔺🔵🔺?. A message at the bottom says 'Find the rule in each sequence, then the missing elements are your keys.' As a codebreaker, explain the rule for each sequence and what the missing elements are.