The largest known prime number is 243112609 - 1, the largest integer that is currently known to be a Prime number. It was proven by Euclid that there are infinitely many prime numbers; thus, there is always a prime greater than the largest known prime.
7919
Yes.
Two.
Nope - it can be divided by 3.
It doesn't have two factors.
No, it is an even number and therefore can be at least divided by 2.
3, 5, and 7.
11/12 cannot be simplified - because 11 is a primenumber.
It's already in its simplest form - 67 is a primenumber.
18/29 cannot be simplified - because 29 is a primenumber !
I could bore you with a long mathematical explanation (ask if you want one), but to simplify things, 2 is a prime number.
It's already in its simplest form - since 43 is a primenumber.