If $2n+1$ and $4n+3$ are prime, then $2n-1$ and $4n+1$ are not when $n>2$ How do you prove that, for $n>2$, if $2n+1$ and $4n+3$ are prime numbers, then $2n-1$ and $4n+1$ are composite numbers?

Hint
think about the terms mod 3.
2n +1 can only be congruent to 2 mod 3. why?
now if it's congruent to 2 mod 3, what are the other two terms congruent to mod 3?
