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Question Number 168042 by cortano1 last updated on 01/Apr/22

  The number of natural number k   such that k∣ n^7 −n for ∀n natural   numbers

$$\:\:{The}\:{number}\:{of}\:{natural}\:{number}\:{k} \\ $$$$\:{such}\:{that}\:{k}\mid\:{n}^{\mathrm{7}} −{n}\:{for}\:\forall{n}\:{natural} \\ $$$$\:{numbers} \\ $$

Commented by Rasheed.Sindhi last updated on 02/Apr/22

Depends upon individual n.

$$\mathcal{D}{epends}\:{upon}\:{individual}\:{n}. \\ $$

Answered by alephzero last updated on 02/Apr/22

n^7  is odd if n is odd and even if  n is even  ⇒ n^7 −n is always even  ⇒ k = 2 ∧ k = 1

$${n}^{\mathrm{7}} \:{is}\:{odd}\:{if}\:{n}\:{is}\:{odd}\:{and}\:{even}\:{if} \\ $$$${n}\:{is}\:{even} \\ $$$$\Rightarrow\:{n}^{\mathrm{7}} −{n}\:{is}\:{always}\:{even} \\ $$$$\Rightarrow\:{k}\:=\:\mathrm{2}\:\wedge\:{k}\:=\:\mathrm{1} \\ $$

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