Here is the complete proof taken from this linkHow do I convince myself that n(1+b) is not prime when b>=1?Here is what I did:if n is 3 and b is 3. Then resulting string 111 111 is prime. Is this how it should be done it in proofs? The way I see is this. If n(1+b) is not proved for even one set of values then I can say it is not prime. Set of values in this case was n =3 & b = 3.Is this approach of understanding poofs is right?
How n (1+b) is not prime?
number theory;primes