with 3 rods (1,2 & 3), the goal is to move a tower of n disks from rod #1 to rod #3. You can move disks only one by one, on the rods. You can't put a disk on a smaller one.
At the beginning, all disks are on rod #1, biggest at the bottom, smallest at the top.
Give the smallest sequence of unused rods for a n disks Hanoi tower problem.