Let a = (11 111), (a total of N 1), find all N, so that a is prime

Only when n = 2, a = 11 is prime, and the others when n > 2 should be composite
When n is a composite number, a must be a composite number, which is easy to prove
When n is prime, except 2
N = 3, a has three 1s, which must be multiples of 3
N2 = 11 -- Prime
N5 = 11111 = 41*271
N7 = 1111111 = 239*4649
N11 = 11111111111 = 21649*513239
N13 = 1111111111111 = 53*79*265371653
N17 = 11111111111111111 = 2071723*5363222357
Whether there are infinite primes in the sequence of 1111,. 1.11111 is still a conjecture

RELATED INFORMATIONS

1. A is a prime less than 10, a + 40 is a prime, a + 80 is a prime, and a is a prime______ ．
2. A is a prime less than 10, a + 40 is a prime, a + 80 is a prime, and a is a prime______ ．
3. If n is prime, N + 2 is prime and N > 10, we prove that N + (n + 2) is a multiple of 12
4. Has the proposition that the multiple of 6 plus one is a prime number been proved?
5. In 0,1,2,3. Of these natural numbers, if there are x prime numbers, a odd numbers, Y composite numbers and B even numbers, then
6. If there are p prime numbers, Q composite numbers, s even numbers and t odd numbers in the first n natural numbers, then (P-T) + (Q-S) =? Strive to be specific
7. At 1, 2, 3 If there are p prime numbers, Q composite numbers, m odd numbers and n even numbers, then (P-M) + (q-n)=______ ．
8. The sum of two adjacent natural numbers is 17, one is prime and the other is composite. What are these two numbers?
9. I am a prime number, my one digit and ten digit are two adjacent composite numbers in the natural number, I am ()
10. The sum of all prime numbers within 10 is______ Is a prime and even number______ ．
11. P is prime 2 ^ P + 3 ^ P = a ^ n prove n = 1
12. Given that n > 1, a > 1 and an-1 is a prime number, find the value of a, and explain that n is also a prime number Is the n-th power of a - 1 is a prime number, not an-1 is a prime number, the above type is wrong
13. Prime guess prime = 2 * prime + prime,
14. How to prove that P = n! - 1 is a prime number
15. If a ^ n - 1 is a prime, prove that a = 2 and N is a prime
16. Is there such a prime number, which is still prime if it is added with 10 and 14 respectively? If so, there are () prime numbers
17. How to quickly verify whether a number is prime Find out a random number, how to quickly determine whether it is a prime? The main idea of the algorithm can be required
18. How to prove whether a number is prime or not in many ways To prove whether a number is a prime, for example, to prove whether the integer n is a prime, let I = 2 and do the divisor in turn until I
19. How to prove that a number is prime?
20. The number a is prime, and both a + 10 and a + 14 are prime. What is the number a?