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I have a question in this lesson:

"Determine all prime numbers that can be written as $ n^{2} - 1 $, for some $ n \in N $"

I tried to make $ n^{2} -1 = (n + 1) (n-1)$, but I didn't get any $n \in N $. Can anyone help me with this? Thanks.

Marina
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1 Answers1

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If $n^2 - 1$ is prime, then at least one of $n+1$ and $n-1$ must be equal to $1$ (and it must be $n-1$ since that is the smaller of the two numbers).

Umberto P.
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