I was surprised to encounter a claim made on the internet that the following number is prime:
9s except for one
8. This 506-digit number didn't look especially prime to me. I couldn't find it in any publicly available lists (which clonk out around 8 or so digits), so I did trial division up to
626543489 and then did Miller-Rabin with 5000 rounds (way overkill). It seems, in-fact, to be prime.
My question is--is there anything significant about this number that would help us realize that it is prime? How was it found?
It's not a Mersenne, Fermat, or Perfect prime, for instance. It's not particularly large (the largest known as of this writing is in the tens of millions of digits), but I suspect the previous and next prime numbers aren't known.