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IMC 2024 Grade 8 — Selection round Question 8

IMC · IMC 2024 Grade 8 — Selection round

Question 8

How many seven-digit numbers use each of $1,2,3,4,5,6,7$ exactly once and have every two consecutive digits relatively prime?
  1. $216$
  2. $840$
  3. $864$
  4. $2520$
  5. $5040$