Question 55
How many ways are there to write all numbers from $1$ to $9$ in the cells of a $3 \times 3$ grid so that for all integers $1 \leq n \lt 9$, the cell labeled $n$ shares an edge with the cell labeled $n+1$?
Math Olympiad Vault · MathNet 2022-part-06 — 196 problems (EN–VI)