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MathNet 2024-part-04 — 168 problems (EN–VI) Question 29

Math Olympiad Vault · MathNet 2024-part-04 — 168 problems (EN–VI)

Question 29

Let $n$ be a positive integer. A grasshopper stands on the number line at the number $1$ and may make either a jump of length $2$ or of length $3$ each time. Each time, the grasshopper must land on an integer from $1$ through $n$ where the grasshopper has not been before. The grasshopper would like to visit all integers from $1$ through $n$ exactly once and land on the number $n$.
Prove that this can be done for all $n \ge 9$.