Question 77
Cunégonde has $n$ blocks of heights $1$ to $n$ and would like to arrange them, one after another, in such a way that her cat can move by jumping from one block to the next, from left to right. Her cat can jump from a block to the next one if the latter is either lower, or higher by $1$, than the previous block. At the start, her cat is on the leftmost block.
In how many ways can Cunégonde arrange her blocks so that her cat can get across all the blocks?
In how many ways can Cunégonde arrange her blocks so that her cat can get across all the blocks?