well, to work out if 1,111,111,111,111,177,777,777,777 is a prime number, we find the square root of it and round it up (so if you have 11.3 round it up to 12) then see if any primes below that number divide into it (i have a bad feeling about this). sqrt(1,111,111,111,111,177,777,777,777)=1054092553389.491 rounded up is 1054092553390. Then i give up and let my brain solidify again and take a nap