##### ###### ##### ### # # ### # # ###### ## ## ## ## ## ## ## # # # # # ## ##### #### ##### # # # # # # # #### ## # ## ## ## ## # # # # # ## ## # ###### ## ### # ### # ######
##### ###### ##### ### # # ### # # ###### ## ## ## ## ## ## ## # # # # # ## ##### #### ##### # # # # # # # #### ## # ## ## ## ## # # # # # ## ## # ###### ## ### # ### # ######
The slow way
The obvious recursive formula is . Base case: . This is correct and simple. To compute , you compute and multiply by . To compute , you compute and multiply by . And so on.
This works, but it makes recursive calls. For , that is calls. Can you do better? Take time to work through examples. Notice what happens when is even: .