Paths on the board#1416
Consider an infinite checkered board.
A path from one cell to another is a sequence of cells, where each pair of consecutive cells are adjacent by side. The length of a path is the number of cells in it, not counting the starting point.
A path is simple if it does not contain any repeated cells.
Fix a cell on the board. How many simple paths of a given length start from this cell?
One integer (0 \leq n \leq 22).
Print the number of simple paths of length starting from the chosen cell.
Example 1
Example 2
Example 3