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Bonjour!
I'm trying this number-theory problem, but i don't have any idea how to solve it.
Can you give me some hints ?

We have got any $\mathbb{Z_+}$ number. Let it be $n$.
Then we must proof that $2 \nmid \sigma(n) \implies n = k^2 \vee n = 2k^2$.
Thanks for any help

3 Answers 3