C
Let $k$ be an even natural number. Show that $3 ^ k + 1$ is divisible by $2$ but not by $4$.
_Replace_ `sorry` _in the template below with your solution. Mathlib version used by the checker is v4.28.0_.
import Mathlib.Algebra.Ring.Parity theorem solution (k : ℕ) (hk : Even k) : 2 ∣ 3 ^ k + 1 ∧ ¬ 4 ∣ 3 ^ k + 1 := sorry
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