If is an integer, then must be divisible by which of the following integers?
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If m ≡ 0 ( m o d 3 ) , then 3 ∣ ( m + 3 ) , so the given expression is divisible by 3 .
If m ≡ 1 ( m o d 3 ) , then 3 ∣ ( m + 5 ) , and the result follows.
If m ≡ 2 ( m o d 3 ) , then 3 ∣ ( m + 1 ) , anew.
Thus, the given product must be divisible by 3.
A single counterexample is enough to show that the expression is not necessary divisible by the other options.
Choose m ≡ 1 ( m o d 3 1 5 ) , then the given product is not divisible by neither 5, 7 nor 9.