Question 93
Let $P_1P_2\dots P_n$ be a regular $n$-gon. A frog situated at a vertex $P_k$ ($1 \le k \le n$) can jump to one of the vertices $P_{k+2}$ or $P_{k-3}$, the indexes being considered modulo $n$. Determine the set of positive integers $n \ge 3$ for which the frog can make $n$ jumps such that it visits all the vertices of the $n$-gon and returns to its starting vertex.
Andrei Eckstein
Andrei Eckstein