Question 31
A $n$-trønder walk is a walk starting at $(0,0)$, ending at $(2 n, 0)$ with no self intersection and not leaving the first quadrant, where every step is one of the vectors $(1,1)$, $(1,-1)$ or $(-1,1)$.
(The figure shows the possible 2-trønder walks.)
Find the number of $n$-trønder walks.
(The figure shows the possible 2-trønder walks.)
Find the number of $n$-trønder walks.