Question

Least value of $n,(n\in N)$ for which $2n+1$ is not a prime is

Answer 1

Putting n=1
2(1) + 1 = 3 , which is a prime number
Putting n=2
2(2) + 1 = 5, which is a prime number
Putting n=3
2(3) +1 = 7, which is a prime number
Putting n=4
2(4) +1 =9
So, $2n+1=9\Rightarrow n=4$