Is this number prime or composite - 1111.....1 (77 1's)

Note: Provide the explanation...

it is a prime number

Prime number 31 can be expressed in the form n^5 -1, where n=2. Are there any other primes that can be expressed this way?

Write 0 and then concatenate the prime numbers in increasing sequence i.e. 0.2357111317192329... Is this number rational or irrational?

Note: Give your reasoning also...