If n is even, then 3n is even, and if 3n is even, then n is even.Ifn is even, it means that we can find k integer
such that n = 2* k. Then n+1=2*k+1 is odd.
3n+1=6k+1=2"(3k)+1 where 3k is an integer so 3n+1
is odd.
3n =2*(3k) is even.
Besides, if n+1 is odd we can find an integer p so
that n+1-2p+1 so n = 2p is even.
3n+1 is odd means that we can find an integer
q such that 3n+1=2q+1 so 3n=2q as 3 is not
dividable by 2, it means that n is a multiple of 2,
then n is even.
3n is even means that we can write 3n = 22 where
z is an integer and again it means that n is a
multiple of 2 and then n is even.
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