# Number Theory: Divisibility.

Show that there are infinite positive integers $$n$$ such that $$n+1$$ divides $$5^n - 1$$.

Note by Lucas Nascimento
1 year, 6 months ago

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By Fermat's little Theorem, all numbers n other the 4 which are 1 less than a prime number satisfies the condition.

- 1 year, 5 months ago

With the exception of 4? No?

- 1 year, 5 months ago

Yes thanks I forgot to mention that.

- 1 year, 5 months ago

Correct.

- 1 year, 5 months ago

Correct!

- 1 year, 5 months ago